U.S. patent number 5,920,532 [Application Number 09/015,061] was granted by the patent office on 1999-07-06 for information pick-up apparatus and optical disk apparatus.
This patent grant is currently assigned to Konica Corporation. Invention is credited to Masaya Kobayashi, Katsuya Yagi, Hiroyuki Yamazaki.
United States Patent |
5,920,532 |
Yagi , et al. |
July 6, 1999 |
Information pick-up apparatus and optical disk apparatus
Abstract
The present invention relates to an optical pick-up apparatus
having a laser beam source and an objective lens to converge the
luminous flux from the laser beam source onto the information
recording surface of an optical information recording medium
through a transparent substrate of the optical information
recording medium such as CDs or DVDs, and specifically relates to a
technology to move a divergence degree changing means such as a
collimator lens or the like, in the direction of the optical axis,
and/or to a technology to move the laser beam source in the
direction of the optical axis, corresponding to the thickness of
the transparent substrate of the optical information recording
medium, in order to read information from plural types of optical
information recording mediums having different transparent
substrate thickness.
Inventors: |
Yagi; Katsuya (Hachioji,
JP), Yamazaki; Hiroyuki (Hachioji, JP),
Kobayashi; Masaya (Hachioji, JP) |
Assignee: |
Konica Corporation (Tokyo,
JP)
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Family
ID: |
27526223 |
Appl.
No.: |
09/015,061 |
Filed: |
January 28, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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637210 |
Apr 24, 1996 |
5754513 |
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Foreign Application Priority Data
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Apr 28, 1995 [JP] |
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7-105463 |
Jul 28, 1995 [JP] |
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7-211259 |
Aug 10, 1995 [JP] |
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7-204496 |
Aug 17, 1995 [JP] |
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7-230683 |
Sep 8, 1995 [JP] |
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7-255723 |
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Current U.S.
Class: |
369/53.22;
369/112.24; G9B/19.017; G9B/7.102 |
Current CPC
Class: |
G11B
7/1376 (20130101); G11B 7/123 (20130101); G11B
19/12 (20130101); G11B 7/139 (20130101); G11B
7/085 (20130101); G11B 7/1381 (20130101); G11B
7/13927 (20130101); G11B 7/13925 (20130101); G11B
2007/0006 (20130101); G11B 7/135 (20130101); G11B
2007/0013 (20130101); G11B 7/0903 (20130101) |
Current International
Class: |
G11B
19/12 (20060101); G11B 7/125 (20060101); G11B
7/00 (20060101); G11B 7/085 (20060101); G11B
7/09 (20060101); G11B 7/135 (20060101); G11B
7/12 (20060101); G11B 003/90 (); G11B 007/00 () |
Field of
Search: |
;369/44.24,54,58,93,94,100,109,110,112,116,117,118,124 |
References Cited
[Referenced By]
U.S. Patent Documents
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5097464 |
March 1992 |
Nishiuchi et al. |
5235581 |
August 1993 |
Miyagawa et al. |
5499231 |
March 1996 |
Fennema et al. |
|
Primary Examiner: Huber; Paul W.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Parent Case Text
This application is a divisional of U.S. patent application Ser.
No. 08/637,210, filed Apr. 24, 1996, now U.S. Pat. No. 5,754,513.
Claims
What is claimed is:
1. An optical pick-up apparatus for reading information from a
plurality of optical information recording mediums having different
transparent substrate thicknesses, comprising:
a laser beam source;
an objective lens for converging a luminous flux from the laser
beam source onto an information recording surface of the optical
information recording medium through a transparent substrate of the
optical information recording medium, the objective lens having an
optical axis; and
moving means for moving the laser beam source along the optical
axis according to a thickness of the transparent substrate of the
optical information recording medium.
2. The optical pick-up apparatus according to claim 1, further
comprising:
a diffraction grating arranged between the objective lens and the
laser beam source; and
an angle adjustment means for adjusting a rotation angle of the
diffraction grating according to a pitch of an information track on
the optical information recording medium.
3. The optical pick-up apparatus according to claim 2, wherein
rotation angle adjustment of the diffraction grating is interlocked
with movement of the laser beam source by the moving means.
4. The optical pick-up apparatus according to claim 1, further
comprising:
light receiving means for receiving luminous flux reflected by the
optical information recording medium and passed through the
objective lens, and
a beam splitter for guiding the reflected luminous flux passing
through the objective lens to the light receiving means.
5. The optical pick-up apparatus according to claim 4, wherein the
beam splitter is a hologram beam splitter.
6. The optical pick-up apparatus according to claim 4, wherein the
laser beam source, the light receiving means, and the beam splitter
are structured integrally and movably.
7. The optical pick-up apparatus according to claim 1, wherein the
objective lens is a positive single lens having a convex first
surface facing the laser beam source and a second surface, the
first and second surfaces being aspherical.
8. The optical pick-up apparatus according to claim 1, further
comprising:
a coupling lens having a positive refractive power, and
said laser beam source moving means also moving the coupling lens
in the direction of the optical axis according to the thickness of
the transparent substrate of the optical information recording
medium.
9. The optical pick-up apparatus according to claim 8, wherein the
coupling lens is spherical.
10. The optical pick-up apparatus according to claim 8, wherein a
lateral magnification of the coupling lens is in the range from
0.48 to 0.85.
11. The optical pick-up apparatus according to claim 1, wherein the
moving means moves the laser beam source between a first position
and a second position located at an objective lens-side and more
distant from the first position.
12. The optical pick-up apparatus according to claim 11, further
comprising:
a divergence degree changing means provided between the laser beam
source and the objective lens.
13. The optical pick-up apparatus according to claim 12, wherein
luminous flux passed through the divergence degree changing means
enters the objective lens as substantially parallel light beams,
when the laser beam source is positioned at the first position.
14. The optical pick-up apparatus according to claim 11, further
comprising:
means for determining a numerical aperture of the luminous flux
incident on the optical information recording medium; and
control means for controlling the means for determining the
numerical aperture according to a pitch of an information track on
the optical information recording medium and for changing the
numerical aperture.
15. The optical pick-up apparatus according to claim 14,
wherein the control means controls the means for determining the
numerical aperture so that an effective numerical aperture at the
laser beam-side in the first position is substantially equal to
that in the second position.
16. The optical pick-up apparatus according to claim 14, wherein
said means for determining the numerical aperture is a
diaphragm.
17. The optical pick-up apparatus according to claim 11, wherein
the moving means moves the laser beam source to the first position
when the transparent substrate of the optical information recording
medium has a first thickness, and moves the laser beam source to
the second position when the transparent substrate of the optical
information recording medium has a second thickness greater than
the first thickness.
18. The optical pick-up apparatus according to claim 17, wherein
the apparatus satisfies the following conditional expressions:
wherein,
where,
d1 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the first
position (mm),
d2 represents the distance from the laser beam source to the
objective lens when the laser beam source is located at the second
position (mm),
t1 represents a first thickness of the transparent substrate of the
optical information recording medium (mm),
t2 represents a second thickness of the transparent substrate of
the optical information recording medium (mm),
n represents a refractive index of the transparent substrate of the
optical information recording medium at a wavelength of the laser
beam source, f.sub.0 represents a focal length of the objective
lens (mm), and
m1 represents a lateral magnification of the objective lens
corresponding to the first position.
19. The optical pick-up apparatus according to claim 17, wherein
the apparatus satisfies the following conditional expressions:
where,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
20. The optical pick-up apparatus according to claim 17, wherein
the apparatus satisfies the following conditional expressions:
where,
d1 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the first
position (mm),
d2 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the second
position (mm),
t1 represents a first thickness of the transparent substrate of the
optical information recording medium (mm),
t2 represents a second thickness of the transparent substrate of
the optical information recording medium (mm),
n represents a refractive index of the transparent substrate of the
optical information recording medium at a wavelength of the laser
beam source,
f.sub.0 represents a focal length of the objective lens (mm),
m1 represents a lateral magnification of the objective lens
corresponding to the first position,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
21. The optical pick-up apparatus according to claim 17, wherein
the apparatus satisfies the following conditional expressions:
where,
m1 represents a lateral magnification of the objective lens
corresponding to the first position,
m2 represents a lateral magnification of the objective lens
corresponding to the second position,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
22. The optical pick-up apparatus according to claim 17, wherein
the apparatus satisfies the following conditional expressions:
where,
f.sub.0 represents a focal length of the objective lens (mm),
m1 represents a lateral magnification of the objective lens
corresponding to the first position,
m2 represents a lateral magnification of the objective lens
corresponding to the second position,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
23. The optical pick-up apparatus according to claim 22, wherein
the apparatus satisfies the following conditional expressions:
24.
24. An information recording medium apparatus for reading
information from a plurality of optical information recording
mediums having different transparent substrate thicknesses, said
apparatus comprising:
a laser beam source;
a beam splitter;
an objective lens for converging a luminous flux from the laser
beam source onto an information recording surface of the optical
information recording medium through a transparent substrate of the
optical information recording medium, the objective lens having an
optical axis;
light receiving means for receiving luminous flux reflected by the
surface of the optical information recording medium and passed
through the objective lens and the beam splitter;
discrimination means for discriminating a thickness of the
transparent substrate of the optical information recording medium;
and
moving means for moving the laser beam source along the optical
axis corresponding to a discrimination result of the discrimination
means.
25. The information recording medium apparatus according to claim
24, further comprising:
a diffraction grating arranged between the objective lens and the
laser beam source; and
angle adjustment means for adjusting a rotation angle of the
diffraction grating according to a pitch of an information track on
the optical information recording medium.
26. The information recording medium apparatus according to claim
25, wherein 0-order light passing through the diffraction grating
is controllably positioned on the information track of the optical
information recording medium.
27. The information recording medium apparatus according to claim
25, wherein the rotation angle adjustment of the diffraction
grating is interlocked with movement of the laser beam source by
the moving means.
28. The information recording medium apparatus according to claim
24, wherein the beam splitter is a hologram beam splitter.
29. The information recording medium apparatus according to claim
24, wherein the laser beam source, the light receiving means and
the beam splitter are structured integrally and movably.
30. Information recording medium apparatus according to claim 24,
wherein the discrimination means discriminates the thickness of the
transparent substrate by use of the operation buttons of the
reading apparatus.
31. The information recording medium apparatus according to claim
24, wherein the discrimination means discriminates the thickness of
the transparent substrate according to signals from the light
receiving means.
32. The information recording medium apparatus according to claim
31, wherein the discrimination means discriminates the thickness of
the transparent substrate from frequency components of the signals
and a rotation speed of the optical information recording
medium.
33. The information recording medium apparatus according to claim
24, further comprising:
an actuator coupled to move the objective lens for focusing and
tracking.
34. The information recording medium apparatus according to claim
24, wherein a control means controls movement of the laser beam
source so as to correct variations of aberration, due to
temperature variations, of a beam spot focused on the optical
information recording medium.
35. The information recording medium apparatus according to claim
24, wherein the objective lens is a positive single lens having a
convex first surface facing the laser beam source and a second
surface, the first and second surfaces being aspherical.
36. The information recording medium apparatus according to claim
24, further comprising:
a coupling lens having a positive refractive power, and
said laser beam source moving means also moves the coupling lens in
the direction of the optical axis according to the thickness of the
transparent substrate of the optical information recording
medium.
37. The information recording medium apparatus according to claim
36, wherein the coupling lens is spherical.
38. The information recording medium apparatus according to claim
36, wherein a lateral magnification degree of the coupling lens is
in a range of 0.48 to 0.85.
39. The information recording medium apparatus according to claim
24, wherein the moving means moves the laser beam source between a
first position and a second position located adjacent to the
objective lens and distant from the first position.
40. The information recording medium apparatus according to claim
39, further comprising:
means for determining a numerical aperture of luminous flux
incident on the optical information recording medium; and
control means for controlling a means for determining a numerical
aperture according to a pitch of an information track on the
optical information recording medium and for changing the numerical
aperture.
41. The information recording medium apparatus according to claim
40, wherein the control means controls the means for determining
the numerical aperture so that an effective numerical aperture at a
laser beam-side in the first position is substantially equal to
that in the second position.
42. The information recording medium apparatus according to claim
39, further comprising:
divergence degree changing means provided between the laser beam
source and the objective lens.
43. The information recording medium apparatus according to claim
42, wherein the luminous flux passing through the divergence degree
changing means enters the objective lens as substantially parallel
light beams.
44. The information recording medium apparatus according to claim
39, wherein the moving means moves the laser beam source to the
first position when the transparent substrate of the optical
information recording medium is of a first thickness, and moves the
laser beam source to the second position when the transparent
substrate of the optical information recording medium is of a
second thickness thicker than the first thickness.
45. The information recording medium apparatus according to claim
24, wherein the apparatus satisfies the following conditional
expressions:
wherein,
where,
d1 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the first
position (mm),
d2 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the second
position (mm),
t1 represents a first thickness of the transparent substrate of the
optical information recording medium (mm),
t2 represents a second thickness of the transparent substrate of
the optical information recording medium (mm),
n represents a refractive index of the transparent substrate of the
optical information recording medium at a wavelength of the laser
beam source,
f.sub.0 represents a focal length of the objective lens (mm),
and
m1 represents a lateral magnification of the objective lens
corresponding to the first position.
46. The information recording medium apparatus according to claim
44, wherein the apparatus satisfies the following conditional
expressions:
where,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
47. The information recording medium apparatus according to claim
44, wherein the apparatus satisfies the following conditional
expressions:
where,
d1 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the first
position (mm),
d2 represents a distance from the laser beam source to the
objective lens when the laser beam source is located at the second
position (mm),
t1 represents a first thickness of the transparent substrate of the
optical information recording medium (mm),
t2 represents a second thickness of the transparent substrate of
the optical information recording medium (mm),
n represents a refractive index of the transparent substrate of the
optical information recording medium at a wavelength of the laser
beam source,
f.sub.0 represents a focal length of the objective lens (mm),
m1 represents a lateral magnification of the objective lens
corresponding to the first position,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
48. The information recording medium apparatus according to claim
44, wherein the apparatus satisfies the following conditional
expressions:
where,
m1 represents a lateral magnification of the objective lens
corresponding to the first position,
m2 represents a lateral magnification of the objective lens
corresponding to the second position,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
49. The information recording medium apparatus according to claim
44, wherein the apparatus satisfies the following conditional
expressions:
where,
f.sub.0 represents a focal length of the objective lens (mm),
m1 represents a lateral magnification of the objective lens
corresponding to the first position,
m2 represents a lateral magnification of the objective lens
corresponding to the second position,
NA1 represents a numerical aperture of the objective lens when the
laser beam source is located at the first position, and
NA2 represents a numerical aperture of the objective lens when the
laser beam source is located at the second position.
50. The optical pick-up apparatus according to claim 49, wherein
the apparatus satisfies the following conditional expressions:
Description
BACKGROUND OF THE INVENTION
The present invention relates to an optical pick-up apparatus and
an optical disk apparatus by which optical information is
reproduced by irradiation of optical beams such as laser beams onto
an optical information recording medium such as optical disk, or
the like.
Conventional technologies related to the present invention will be
described below.
In FIG. 16, luminous flux emitted from a laser beam source 1 passes
through a beam splitter 2, enters into a collimator lens 3, and is
emitted as parallel luminous flux. This luminous flux is limited to
a predetermined luminous flux by a diaphragm, and enters into an
objective lens 6. When parallel luminous flux enters into the
objective lens 6, the objective lens 6 forms an optical spot image,
having no aberration, onto a information recording surface 8
through a substrate 7 having a predetermined thickness (herein,
t=0.6 mm).
The luminous flux, which is modulated by information pits and
reflected on this information recording surface 8, returns to the
beam splitter 2 through the objective lens 6 and the collimator
lens 3, is separated from the optical path of the laser beam source
1, and enters into a receiving means 9. This receiving means 9 is
composed of PIN photo-diodes which are divided into a plurality of
elements, and a current which is proportional to the strength of
the entered luminous flux, is outputted from each element. This
current is sent to a detection circuit system, not shown in the
drawing, and an information signal, a focus error signal and a
track error signal are generated in this detection circuit system.
The objective lens 6 is controlled by a two-dimensional actuator,
not shown in the drawing, composed of a magnetic circuit, a coil,
or the like, according to the focus error signal and the track
error signal, so that the optical spot position is always focused
on the information track.
A large numerical aperture (for example, NA 0.6) is used in such an
optical pick-up apparatus so that the diameter of an optical spot,
collected by the objective lens 6, is reduced. Accordingly, when
the thickness of the substrate 7, which is placed in the converging
luminous flux, deviates from a predetermined thickness, large
spherical aberrations are generated.
Referring to FIG. 17, this aberration will be explained. When the
thickness of the substrate is changed in the objective lens, which
is optimized under the condition that NA is 0.6, the wavelength of
the laser beam emitted from the laser beam source is 635 nm, the
thickness of the substrate is 0.6 mm, and the refractive index is
1.58, then, the aberration is increased by 0.01 .lambda.rms per
0.01 mm deviation. When the thickness of the substrate deviates by
.+-.0.07 mm, the aberration is increased by 0.07 .lambda.rms, and
reaches the Marechal criterion which is a value within which
reading and writing operations can normally be performed.
Accordingly, when a information recording medium, made of a 1.2 mm
thickness substrate, is used for reproduction instead of a
information recording medium which is made of a 0.6 mm thickness
substrate, an objective lens 36 and a diaphragm 35 corresponding to
the 1.2 mm thickness substrate are provided in addition to the
objective lens 6 corresponding to a 0.6 mm thickness substrate in
the two-dimensional actuator portion, and the objective lens and
the diaphragm are switched to the objective lens 36 and the
diaphragm 35 for reproduction.
Alternatively, the following is also considered. Two optical
pick-up apparatus respectively used for an information recording
medium made of a 0.6 mm thickness substrate and for an information
recording medium made of a 1.2 mm thickness substrate, are provided
in a single optical disk apparatus.
Further, the following is also considered. A hologram is provided
in the optical pick-up apparatus, and a 0-order light and a
1st-order light which transmit the hologram, are respectively used
as optical spots corresponding to the 0.6 mm thickness substrate
and the 1.2 mm thickness substrate, and these optical spots are
converged on the information recording surface.
As described above, in an apparatus in which two objective lenses
respectively corresponding to 0.6 mm and 1.2 mm thickness
substrates are provided, or two optical pick-up apparatus for the
0.6 mm and for 1.2 mm thickness substrates are used, in order to
reproduce an information recording medium having different
thickness substrates in one optical disk apparatus, it is
impossible to produce a compact optical pick-up apparatus and an
optical disk apparatus low in cost.
Further, even when the thickness of the substrate is the same, in
cases of information recording mediums (for example, CDs, DVDs) in
which difference of the image recording density is large, the size
of the spot to be read is inappropriate for the information pit
size, resulting in a decrease of reproduction performance.
In the method in which a hologram is provided in the optical
pick-up apparatus, and a 0-order light and a 1st-order light which
transmit the hologram, are respectively used as optical spots
corresponding to the 0.6 mm thickness substrate and the 1.2 mm
thickness substrate, and these optical spots are converged onto the
information recording surface, since two luminous flux are always
sent to the information recording surface of the information
recording medium, one luminous flux is not necessary for
information reading out when information reading out is carried out
by the optical spot of another luminous flux, resulting in increase
of noise. Further, since the laser beam strength is used under
divided condition, the S/N ratio is decreased by a corresponding
decrease of the amount of light, or the life of the laser beam is
decreased as the amount of light is increased. Further, in the
method in which recording is carried out, since a loss of light
emission is increased, a higher output laser apparatus is required,
resulting in a further increase of cost.
Further, in cases where track errors are detected by a 3-beam
method, when the number of types of azimuth of 3 beams is one with
respect to information tracks on the optical disk, track error
signals can not be detected effectively with respect to both
optical disks having different track pitches (for example, 0.84
.mu.m and 1.6 .mu.m), and thus the tracking performance is
reduced.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a simple
structure and compact optical pick-up apparatus and optical disk
apparatus, which can reproduce information from information
recording mediums having different substrate thickness, by a single
optical pick-up apparatus, and which are interchangeable with each
other.
The second object of the present invention is to provide an optical
disk apparatus in which a driving method for the optical pick-up
correction means, including therein a correction means, is
simplified and optimized to satisfactorily adapt to information
recording mediums having different substrate thickness to the
system, and further, an information recording medium apparatus
which is compact and inexpensive, and by which information
recording mediums having different substrate thickness, can be
reproduced or be recorded on with a single apparatus.
The first embodiment to attain the first object of the present
invention is an optical pick-up apparatus by which information from
a plurality of optical information recording mediums having
different transparent substrate thickness is read, and which
comprises:
a laser beam source;
an objective lens to converge a luminous flux from the laser beam
source onto the information recording surface of the optical
information recording medium through a transparent substrate of the
optical information recording medium; and
a moving means for moving a divergence degree changing means in the
direction of the optical axis of a luminous flux from the laser
beam source corresponding to the thickness of the transparent
substrate of the optical information recording medium, wherein the
divergence degree changing means changes the divergence degree of
the luminous flux from the laser beam source, which enters into the
objective lens, by movement by the moving means.
The second embodiment to attain the object of the present invention
is an information recording medium apparatus by which information
from a plurality of optical information recording mediums having
different transparent substrate thickness is read, and which
comprises:
a laser beam source;
a beam splitter;
an objective lens to converge a luminous flux from the laser beam
source onto the information recording surface of the optical
information recording medium through a transparent substrate of the
optical information recording medium;
a light receiving means for receiving the luminous flux which has
been reflected by the surface of the optical information recording
medium and passed through the objective lens and the beam
splitter;
a discrimination means for discriminating the thickness of the
transparent substrate of the optical information recording medium;
and
a moving means for moving a divergence degree changing means in the
direction of the optical axis of a luminous flux from the laser
beam source corresponding to the result of discrimination by the
discriminationg means,
wherein the divergence degree changing means changes the divergence
degree of the luminous flux from the laser beam source, which
enters into the objective lens, by movement by the moving
means.
The third embodiment to attain the object of the present invention
is an optical pick-up apparatus by which information from a
plurality of optical information recording mediums having different
transparent substrate thickness is read, and which comprises:
a laser beam source;
an objective lens to converge a luminous flux from the laser beam
source onto the information recording surface of the optical
information recording medium through a transparent substrate of the
optical information recording medium; and
a moving means for moving a laser light source in the direction of
the optical axis corresponding to the thickness of the transparent
substrate of the optical information recording medium.
The fourth embodiment to attain the object of the present invention
is an information recording medium apparatus by which information
from a plurality of optical information recording mediums having
different transparent substrate thickness is read, and which
comprises:
a laser beam source;
a beam splitter;
an objective lens to converge a luminous flux from the laser beam
source onto the information recording surface of the optical
information recording medium through a transparent substrate of the
optical information recording medium;
a light receiving means for receiving the luminous flux which has
been reflected by the surface of the optical information recording
medium and passed through the objective lens and the beam
splitter;
a discrimination means for discriminating the thickness of the
transparent substrate of the optical information recording medium;
and
a moving means for moving the laser beam source in the direction of
the optical axis corresponding to the result of discrimination by
the discriminationg means.
In the first and second embodiments, the divergence degree changing
means can move between the first position on the objective lens
side and the second position on the laser beam source side on the
optical axis between the objective lens and the laser beam source
by the moving means.
The moving means moves the divergence degree changing means to the
first position when the transparent substrate of the optical
information recording medium has the first thickness, and moves the
divergence degree changing means to the second position when the
transparent substrate of the optical information recording medium
has the second thickness which is thicker than the first
thickness.
In the third and fourth embodiments, the laser beam source can move
between the first position and the second position, which is closer
to the objective lens than the first position.
The moving means moves the laser beam source to the first position
when the transparent substrate of the optical information recording
medium has the first thickness, and moves the laser beam source to
the second position when the transparent substrate of the optical
information recording medium has the second thickness, which is
thicker than the first thickness.
As described above, when the divergence degree changing means or
the laser beam source is moved, the divergence degree of the
luminous flux entering into the objective lens is changed, and the
spherical aberration due to the difference of thickness of the
transparent substrates of the optical information recording medium
is corrected, resulting in excellent reading performance.
Further, in the first to fourth embodiments, the apparatus includes
a control means for changing the numerial aperture by controlling a
means for determining the numerial aperture of the luminous flux
entering into the optical information recording medium, and a means
for determining the numeral aperture corresponding to pitches of
the information track of the optical information recording medium,
and the reading characteristics due to the difference of the track
pitches are optimized in addition to correction of the difference
of the thickness of the substrate.
A diffraction lattice is arranged between the objective lens and
the laser beam source, and an angle adjusting means for adjusting
the rotation angle of the diffraction lattice corresponding to
pitches of the information track of the optical information
recording medium is provided, so that an optimum track error signal
is detected by the three-beam method, and stable tracking
performance can be attained.
The second and fourth embodiments are information recording medium
apparatus using the optical pick-up in the first and third
embodiments.
The discrimination means descriminates the thickness of the
transparent substrate based on the input from operation buttons of
the reading apparatus, or signals from the light receiving means,
by frequency component of the signals and the rotation speed of the
optical information recording medium. The divergence degree
changing means or the laser beam source is moved by the control
means for controlling the movement of the moving means, and the
optimum reading performance is attained with respect to the
thickness of the transparent substrates.
Further, when the movement of the moving means is controlled so as
to compensate for changes of aberration of the beam spot, focused
on the optical information recording medium, due to temperature
variations, the optimum information reading performance or the
optimum writing performance can be attained.
According to the present invention, information from the
information recording mediums having different substrate thickness
can be reproduced by changing the divergence degree of the luminous
flux from the laser beam source, which enters into the objective
lens, corresponding to the thickness of the transparent substrates
of the optical information recording mediums.
FIG. 1 is a view of an optical path in cases where the luminous
flux enters into an objective lens 6 in which the aberration
compensation is optimized when a parallel luminous flux of the
wavelength of 635 nm enters into the lens under the conditions that
NA is 0.60, the thickness of the substrate is 0.60 mm, and the
refractive index is 1.58. The luminous flux from the point at
infinity is converged onto a position (the rear surface of a
substrate 7) corresponding to a information recording surface 8
through a diaphragm 5, an objective lens 6, and a substrate 7.
Relating such the objective lens 6, the objective lens of the
wavefront aberration of 0.000 .lambda.rms, can be attained when an
aspherical surface is utilized for the lens.
FIG. 2 shows the relationship between the thickness of the
substrate and the divergence degree when this objective lens 6 is
used. The horizontal axis shows the thickness of the substrate, and
the vertical axis shows the magnification ratio (the magnification
ratio between the laser beam source and the optical spot to be
converged, which are viewed by the objective lens) of the objective
lens in its working condition, which is a function of the
divergence degree of the luminous flux entering into the objective
lens. The luminous flux passing through the objective lens to the
substrate is always converged, and the sign when the converged
light enters into the objective lens, is denoted by +, and the
sign, when the divergence light enters into the objective lens, is
denoted by -. When the magnification ratio is 0, parallel light
beams enter into the objective lens.
The curve shown in the drawing, is obtained by connecting the
magnification ratios, in which the wavefront aberration is minimum,
with respect to the thickness of the substrates. In substrates of
0.60 mm thickness, which is the reference, when the thickness of
the substrate is increased in cases where parallel light beams
enter into the objective lens, the aberration is reduced when minus
light beams, that is, the diverged light, enter into the objective
lens. In cases where the thickness of the substrate is decreased,
the aberration is reduced when plus light beams, that is, the
converged light, enter into the objective lens.
FIG. 3 shows a case in which the diverging light is caused to enter
into the objective lens 6 when the thickness of the substrate is
increased. When the thickness of the substrate is increased, the
spherical aberration becomes overcorrected due to the increased
amount of the thickness. However, it is canceled by generating
undercorrected spherical aberration by the objective lens when the
diverging light is caused to enter into the objective lens.
When the magnification ratio between the laser beam source and the
optical spot formed on the information recording surface is -0.089,
in cases where the same objective lens as described above is used
and NA is 0.60, the thickness of the substrate is 1.61 mm, then,
the wavefront aberration is 0.03 .lambda.rms, and is corrected so
as to be sufficient for the information reproduction.
FIG. 4 shows a case in which the converged light is caused to enter
into the objective lens 6 when the thickness of the substrate is
reduced. An undercorrected spherical aberration generated by an
amount of the reduction of the thickness of the substrate, is
canceled by generating an overcorrected spherical aberration by
entering the converged light into the objective lens. When the
magnification ratio between the laser beam source and the optical
spot on the information recording surface is +0.112, in cases where
NA is 0.60 and the thickness of the substrate is 0.10 mm, then, the
wavefront aberration is 0.03 .lambda.rms. In this connection, the
diaphragm 5 is placed at a frontal focus point of the objective
lens 6 commonly in FIGS. 1, 3 and 4, and the diaphragm 5 has the
same diameter in all cases.
An optical system of an optical pick-up apparatus of the present
invention, comprises: a laser beam source; a lens to reduce the
divergent angle of the light beam diverged from the laser beam
source; and an objective lens having a positive refractive power by
which the outgoing beam from the lens is converged onto the
information recording surface through a transparent substrate of
the optical information recording medium, and the optical system of
an optical pick-up apparatus is characterized in that the
divergence degree changing lens is moved in the direction of the
optical axis corresponding to the thickness of the transparent
substrate, and satisfies the following condition.
Where,
d.sub.1, d.sub.2 : the distance from the laser beam source to a
point at which the surface of the divergent degree changing lens,
which is the closest to the light beam source, crosses with the
optical axis, when the thickness of the transparent substrates is
respectively t.sub.1 and t.sub.2, and t.sub.1 <t.sub.2.
The above-described objective lens is a positive single lens in
which the convex surface of the lens is opposite to the light beam
source, and both surface respectively opposite to the light beam
source side and the information recording surface side are
aspherical surface, and the lens is made of glass or a plastic
material.
Further, this optical system is preferably structured such that the
luminous flux outgoing from the divergence degree changing lens and
entering into the objective lens is almost parallel with each other
when the divergence degree changing lens is located at D.sub.1.
FIG. 18 shows the amount of spherical aberration generated when the
divergence degree changing lens moves along the optical axis, in
the optical system in which the aberration correction is optimized
with respect to a 0.6 mm thick substrate in Example 8. When the
divergence degree changing lens is moved along the optical axis
from a predetermined angle to the light beam source (when the
parallel light beams go out), an angle of emergence of the luminous
flux outgoing from the divergence degree changing lens is larger
than the angle of emergence before the movement, and the luminous
flux having a divergent degree larger than the optimum condition,
enters into the objective lens, resulting in an undercorrected
spherical aberration. When the divergence degree changing lens is
moved along the optical axis from a predetermined position to the
objective lens, the angle of emergence of the luminous flux
outgoing from the divergence degree changing lens is smaller than
the angle of emergence before the movement, and luminous flux
having a divergent degree smaller than the optimum condition enters
into the objective lens, resulting in an overcorrected spherical
aberration.
As described above, in the optical system which is optimized with
respect to a predetermined substrate thickness, the more the
thickness of the substrate is increased, and the further, is the
distance of the divergence degree changing lens from the light beam
source, the more the spherical aberration is overcorrected.
Reversely, the more the thickness of the substrate is decreased,
and the shorter is the distance of the divergence degree changing
lens from the light beam source, the more the spherical aberration
is undercorrected. Accordingly, the overcorrected spherical
aberration generated in cases where the thickness of the substrate
is increased, can be canceled by generating an undercorrected
spherical aberration when the divergence degree changing lens is
closer to the light beam source. Reversely, the undercorrected
spherical aberration, generated in cases where the thickness of the
substrate is decreased, can be canceled by generating an
overcorrected spherical aberration when the divergence degree
changing lens is located farther from the light beam source.
When the surface on the side of the light beam source of the
objective lens is convex, and further if an aspherical surface is
used for the objective lens, the objective lens used in the present
invention can be realized as a single lens, resulting in decreased
cost. In this case, although glass or resin is suitable as the
material for the objective lens, resin is preferable because of
reduction of cost.
Further, the optical system preferably satisfies the following
conditional expressions. ##EQU1## where,
d.sub.1 : the distance (DVD) from the laser beam source to the
first position (mm)
d.sub.2 : the distance (CD) from the laser beam source to the
second position (mm)
t.sub.1 : the first thickness of the transparent substrate of the
optical information recording medium (mm)
t.sub.2 : the second thickness of the transparent substrate of the
optical information recording medium (mm)
n: the refractive index of the transparent substrate of the optical
information medium at the wavelength of the light beam source
f.sub.0 : the focal length of the objective lens (mm)
f.sub.c : the focal length of the divergent degree changing lens
(mm)
fT: the focal length of the entire optical system at the thickness
of the transparent substrate of t.sub.1. (mm)
The spherical aberration generated by variations .DELTA.t of the
thickness of the substrate, is sufficiently corrected in the entire
optical system by generating the reverse spherical aberration, when
the divergence degree changing lens having a focal length of
f.sub.c is moved along the optical axis. At this time, the larger
the expression {(n.sup.2 -1)/n.sup.3 }.DELTA.t is, the larger the
movement amount .DELTA.d of the divergence degree changing lens is,
and this relationship is proportional. An amount of the spherical
aberration which can be corrected by the movement of the divergence
degree changing lens, is inversely proportional to (f.sub.o /fT)
and (f.sub.0 /f.sub.c).sup.2.
From the foregoing, regarding the amount of the movement of the
divergence degree changing lens which is moved to correct the
spherical aberration generated by a change of the thickness of the
transparent substrate of the optical information recording medium,
it is preferable that a value normalized by the above-described
expressions, {(n.sup.2 -1)/n.sup.3 }.DELTA.t, (f.sub.o /fT) and
(f.sub.0 /f.sub.c).sup.2, is within the range of Equation (1).
When this lens is moved beyond the upper limit, the spherical
aberration becomes undercorrected, and exceeds the Marechal
criterion which is a criterion for the limit of diffraction.
Conversely, when the lens is moved reversely below the lower limit,
the overcorrected spherical aberration generated at .DELTA.t is not
sufficiently corrected, and also exceeds the Marechal criterion.
Therefore, the diameter of the spot can not satisfactorily
reduced.
The optical system of the optical pick-up apparatus, relating to
the third or fourth embodiment to attain the first object of the
present invention, is structured as follows. The optical system of
the optical pick-up apparatus comprises: at least a laser beam
source; and a finite conjugate type objective lens having the
positive refractive power to converge the luminous flux emitted
from the light beam source onto the information recording surface
through a transparent substrate of the optical information
recording medium, and the recording and reproducing optical system
is characterized in that the laser beam source is moved along the
optical axis corresponding to the thickness of the transparent
substrate, and the optical system satisfies the following
relationship,
where,
mti: the lateral magnification of the entire system from the laser
beam source to the information recording surface of the optical
information recording medium, and the thickness ti, of the
transparent substrate, has the following relationship,
In the objective lens which converges the luminous flux onto the
information recording surface, both surfaces on the side of the
light beam source and on the side of the information recording
surface, are aspherical, and the surface on the side of the light
beam source is a convex surface. The objective lens is
characterized in satisfying the following relationship,
wherein,
where,
.DELTA.d=d2-d1
.DELTA.t=t2-t1
d1: the interval between the laser beam source located at the first
position and the objective lens (mm)
d2: the interval between the laser beam source located at the
second position and the objective lens (mm)
t.sub.1 : the first thickness of the transparent substrate of the
optical information recording medium
t.sub.2 : the second thickness of the transparent substrate of the
optical information recording medium
n: the refractive index of the transparent substrate of the optical
information recording medium at the wavelength of the laser beam
source
f.sub.0 : the focal length of the objective lens
m1: the lateral magnification of the objective lens corresponding
to the first position
When the numerical aperture on the side of the information
recording surface of the objective lens is denoted as NA1 at the
first thickness of the transparent substrate, and NA2 at the second
thickness, which is thicker than the first thickness, the numerical
aperture is characterized in satisfying the following
relationship,
Further,
when
then,
The above-described objective lens is characterized in satisfying
the following relationships,
Where,
NA1: the numerical aperture on the side of the information
recording surface at the thickness of t1(<t2) of the transparent
substrate
NA2: the numerical aperture on the side of the information
recording surface at the thickness of t2 of the transparent
substrate
m1: the lateral magnification of the objective lens at the
thickness of t1 of the transparent substrate
m2: the lateral magnification of the objective lens at the
thickness of t2 of the transparent substrate
The above-described objective lens is characterized by satisfying
the following relationship,
Further, the above-described objective lens preferably satisfies
the following relationship,
An object of the optical system of the optical pick-up apparatus of
the present invention is to satisfactorily correct the spherical
aberration generated by the change of .DELTA.t of the thickness of
the substrate by being canceled with the spherical aberration
generated in the objective lens by the movement of the light beam
source along the optical axis.
Actually, an amount of change .DELTA.Sat of the spherical
aberration with respect to the change .DELTA.t of the thickness of
the substrate is proportional in the case of the same NA, and can
be expressed as follows.
Herein, n is a refractive index at the wavelength of the light beam
source of the transparent substrate.
It can be considered that the change of magnification .DELTA.m of
the single lens type objective lens and the amount of change of
.DELTA.SAm of the spherical aberration by the change of
magnification .DELTA.m are almost proportional.
Herein, f.sub.0 is a focal length of the objective lens.
Therefore, the following relationship may be satisfied in order to
entirely correct the spherical aberration,
That is,
In this case, in Equation (11), when n is constant and .DELTA.t is
positive (>0), the spherical aberration is increased. That is,
.DELTA.SAt>o. As a result, since n>1, the constant a becomes
positive.
Further, in Equation (12), when a change of the lateral
magnification is positive (.DELTA.m>0) in the change of the
lateral magnification .DELTA.m (when an absolute value of the
lateral magnification in a real image system, not in a reflection
system, is reduced), the spherical aberration is increased.
Therefore, .DELTA.Sam>0. As a result, since f.sub.0 >0, the
constant .beta. is positive.
As a result, when .DELTA.t (=t2-t1>0) is positive, .DELTA.m is
negative (<0) from Equation (14).
When the lateral magnification in which the spherical aberration is
corrected best at the transparent substrate thickness of t1, is m1,
and the lateral magnification in which the spherical aberration is
corrected best at the transparent substrate thickness of t2
(t2>t1, .DELTA.t=t2-t1), is m2, then, the following equation is
obtained,
As a result, the following relationship is obtained,
The spherical aberration of the objective lens can be
satisfactorily corrected when the surface on the side of the light
beam source, of the objective lens, is the convex surface, and both
lens surfaces are aspherical.
In order to satisfactorily correct the spherical aberration
.DELTA.SAt generated when the thickness of the transparent
substrate changes (.DELTA.t), the relationship between the amount
of the movement .DELTA.d of the light beam source and a change
.DELTA.m of the lateral magnification ratio of the objective lens
is found.
The amount of movement .DELTA.d of the light beam source can be
expressed as follows:
Herein, f.sub.0 is the focal length of the objective lens.
Equation (17) is transformed as follows:
When Equation (18) is substituted into Equation (15), then,
When the above Equations are substituted into Equation (14), the
relationship among .DELTA.d, .DELTA.t and the objective lens is
expressed as follows,
Herein, in order to simplify the left side of equation (20), the
left side is expressed by G. That is,
It is necessary to set G by changing the spherical aberration
.DELTA.d generated due to the change .DELTA.t of the thickness of
the substrate so that the allowable error is suppressed within the
spherical aberration of 0.045 .lambda.rms as the wavefront
aberration value after allowable values, such as production errors
or the like, are subtracted from the Marechal criterion (the
wavefront aberration of 0.07 .lambda.rms) as a target value to be
compensated for.
When .DELTA.d is set so that G exceeds the upper limit (-0.5) of
the conditional expression (2), the spherical aberration enters
into the "under" range, and the spherical aberration exceeds 0.045
.lambda.rms even when NA2 is as small as 0.3. When .DELTA.d is set
so that G is reduced smaller than the lower limit of -2.1, the
spherical aberration enters into the "overcorrected" range, and the
spherical aberration exceeds 0.045 .lambda.rms, even when NA2 is
about 0.3.
When NA2 is increased to larger than 0.50 (conditional expression
(5')), it is difficult to maintain the spherical aberration within
0.045 .lambda.rms if G is not within the range from -1.5 to -0.8
(conditional expression (2')).
Specifically, when G is larger than -1.3 and smaller than -1.0, the
spherical aberration is close to 0, resulting in excellent
performance.
Further, when NA1 and NA2 exceed 0.65, excellent performance is not
attainable.
When the numerical aperture of the side of the light beam source is
NA.sub.0 1 at the first position (the position at t1), and the
numerical aperture of the side of the light beam source is NA.sub.0
2 at the second position (the position at t2), NA.sub.0 1, and
NA.sub.0 2 are required to satisfy the following relationship,
When respective numerical apertures are smaller than 0.035, the
utilization efficiency of the laser beam is reduced due to the
divergent angle of the laser beam, and sufficient light intensity
is not obtained for recording and reproducing optical information
recording medium. When respective numerical apertures are larger
than 0.15, the diameter of the spot is not reduced for recording
and reproducing optical information recording medium due to the
divergent angle of the laser beam, astigmatic difference of the
laser beam, and oval-shaped light amount distribution.
The numerical aperture (NA01, NA02) of the light beam source-side
can be expressed by a product of the numerical aperture on the
information recording surface-side and an absolute value of the
lateral magnification ratio (m1, m2) of the optical system. That
is,
Conditional expressions (6) and (7) are obtained when the above
expressions (24) and (25) are substituted into the expressions (22)
and (23).
Here, the following expressions are obtained in order to convert
the light beams diverged from the light beam source into converged
light beams by the objective lens,
The distance from the light beam source to the information
recording surface is changed by unintentional movement, or the
like, of the transparent substrate of the optical information
recording medium, and spherical aberration due to change of the
distance between the light beam source and image, is generated when
the objective lens is driven so that automatic focusing is carried
out on the change of the distance.
If .vertline.m1.vertline..multidot.f.sub.0 .multidot.NA1.sup.4
exceeds 0.061 at the first arrangement position, the amount of
generation of the spherical aberration due to change of the
distance between the light beam source and the image, exceeds the
allowable value (conditional expression (9)).
If .vertline.m2.vertline..multidot.f.sub.0 .multidot.NA2.sup.4
exceeds 0.061 at the first arrangement position, an amount of
generation of the spherical aberration due to change of the
distance between the light beam source and the image, also exceeds
the allowable value (conditional expression (10)).
Reversely, when .vertline.m1.vertline..multidot.f.sub.0
.multidot.NA1.sup.4 and .vertline.m2.vertline..multidot.f.sub.0
.multidot.NA2.sup.4 are less than 0.045 at the first arrangement
position and the second arrangement position, further excellent
performance can be maintained (conditional expressions (9') and
(10')).
An optical system of the optical pick-up apapratus, according to
the embodiment to attain the first object of the present invention,
comprises: a laser beam source; a coupling lens having the positive
refractive power to convert the divergent angle of the divergent
light from the laser beam source into a smaller one; and an
objective lens having a positive refractive power which converges
the luminous flux outgoing from the coupling lens onto the
information recording surface through the transparent substrate of
the optical information recording medium, wherein the laser beam
source and the coupling lens integrally move along the optical axis
corresponding to the thickness of the transparent substrate, and
satisfy the following condition,
where,
mti: the lateral magnification ratio of the entire optical system
from the laser beam source to the transparent substrate (the
thickness of which is ti), and t1<t2.
In the above-described objective lens, the surface on the side of
the light beam source and the information recording surface are
aspherical, and the surface on the side of the light beam source is
convex. Then, the objective lens is characterized in satisfying the
following relationship,
herein,
where,
d1: the interval from the emergent surface of the coupling lens to
the incident surface of the objective lens when the laser beam
source is located at the first position (DVD) (mm)
d2: the interval from the emergent surface of the coupling lens to
the incident surface of the objective lens when the laser beam
source is located at the second position (DVD) (mm)
t1: the first thickness of the transparent substrate of the optical
information recording medium (mm)
t2: the second thickness of the transparent substrate of the
optical information recording medium (mm)
m.sub.0 1: the lateral magnification of the objective lens single
body in which the wavefront aberration is best at a transparent
substrate thickness of t1.
f.sub.0 : the focal length of the objective lens
n: the refractive index of the transparent substrate at the
wavelength of the light beam source
Further, in the above-described objective lens, when the numerical
aperture of luminous flux converging the light beam onto the image
recording surface is NA1 at the first thickness of the transparent
substrate, and NA2 at the second thickness which is thicker than
the first thickness, then, the objective lens satisfies the
following conditions,
However, when
the objective lens preferably satisfies the following
condition,
The optical system of the optical pick-up apparatus using the
above-described objective lens is characterized in satisfying the
following condition,
mt1: the lateral magnification ratio of the entire optical system
in which the wavefront aberration is minimum when the transparent
substrate, the thickness of which is minimum, of the optical
information medium is used. Specifically, it is preferable to
satisfy the following condition,
When the above-described objective lens is made of glass, the
following condition is preferably satisfied,
m.sub.0 1: the lateral magnification ratio of the objective lens
single body with respect to the lateral magnification ratio mt1 of
the entire optical system in which the wavefront aberration is
minimum when the transparent substrate, the thickness of which is
minimum, of the optical information medium is used.
When the objective lens is made of resin material, the objective
lens preferably satisfies the following condition,
The coupling lens is a spherical lens and the following condition
is satisfied,
m.sub.c : the lateral magnification ratio of the coupling lens
which integrally moves with the light beam source along the optical
axis.
When the aperture diameter at the arrangement position at the first
thickness of the transparent substrate is .phi.A1, and the aperture
diameter at the arrangement position at the second thickness, which
is larger than the first thickness, is .phi.A2, then, it is
preferable that the aperture diameter is adjustable such that
In the optical system of the optical pick-up apparatus of the
present invention, the spherical aberration generated due to the
change of the thickness .DELTA.t of the transparent substrate is
compensated for when the light beam source and coupling lens are
integrally moved along the optical axis, so that the condition is
maintained in which the aberration is satisfactorily corrected
without depending on the change of the thickness of the transparent
substrate.
An amount of change .DELTA.SAt.sub.0 of the spherical aberration is
proportional to the change .DELTA.t of the thickness of the
transparent substrate at the same NA, and can be expressed as
follows when the refractive index of the transparent substrate is
n, and the proportional constant is .alpha..sub.0,
Further, in this optical system, the spherical aberration can also
be generated when the lateral magnification ratio mt1 is changed to
mt2.
When the magnification of the coupling lens is m.sub.c, the lateral
magnification of the objective lens is m.sub.o, the lateral
magnification ratio of the entire optical system is mt, and the
light beam source is integrally moved with the coupling lens, then,
the magnification m.sub.c of the coupling lens is always constant,
and mt is proportional to m.sub.o.
Accordingly, in relation to the amount of th movement .DELTA.d to
correct the spherical aberration, the amount of movement, when the
coupling lens and the light beam source are integrally moved in the
above optical system, the magnification of which is mt, and which
includes the coupling lens, can be considered to be the same as the
amount of movement when only the light beam source is moved in the
optical system, the magnification of which is m.sub.o, and which
does not include the coupling lens.
Accordingly, the amount of .DELTA.d does not depend on the coupling
lens, and depends on only the objective lens.
Further, a change of magnification of the single-lens objective
lens .DELTA.m.sub.0 and the amount of the change of the spherical
aberration .DELTA.SAm.sub.0 due to the change of magnification of
the single-lens objective lens .DELTA.m.sub.0, are considered to be
almost proportional.
Where, f.sub.0 is the focal length of the objective lens, and
.beta..sub.0 is a proportional constant.
In order to correct the entire change of the spherical aberration,
the following equation may be satisfied.
That is,
In this case, when n is constant and .DELTA.t is positive (>0)
in the equation (41), the spherical aberration moves to an
"overcorrected"-range. Therefore, .DELTA.SAt.sub.0 >0, and
n>1. Accordingly, the constant .alpha..sub.0 is positive.
When, in the equation (42), the change of the lateral magnification
ratio .DELTA.m.sub.0 is positive (m>0), (when an absolute value
of the lateral magnification ratio is reduced in the case of a real
image system, not a reflection system,), then, the spherical
aberration moves toward the "overcorrected"-range. Therefore,
.DELTA.SAm.sub.0 >0, and then, f.sub.0 >0, and the constant
.beta..sub.0 is positive.
As a result, when .DELTA.t is positive, .DELTA.m.sub.0 is negative
(<0), as derived from the equation (44).
At this time, when the lateral magnification ratio in which the
spherical aberration at the transparent substrate t1 is corrected
best, is represented by m.sub.0 1, and the lateral magnification
ratio in which the spherical aberration at the transparent
substrate t2 (t2>t1, .DELTA.t=t2-t1) is corrected best, is
represented by m.sub.0 2, the following equation is obtained,
then,
As a result,
As described above, the relationship between the lateral
magnification ratio mt of the entire optical system and the lateral
magnification ratio of the objective lens single body, is obtained
as follows,
Since the lateral magnification ratio m.sub.c of the coupling lens,
which is viewed from the side opposite to the light beam source, is
always constant and positive (m.sub.c >0), the following
expression is obtained.
The spherical aberration of the objective lens is satisfactorily
corrected when the surface on the side of the light beam source, of
the objective lens is formed as a convex surface, and both surfaces
are aspherical. The influence due to the change of temperature on
the aberration can be reduced when glass material is used. When a
resin material is used, the weight of the objective lens can be
reduced and its cost can be reduced.
In order to satisfactorily correct the spherical aberration
.DELTA.SAt.sub.0 generated due to the change of the transparent
substrate thickness, the relationship between the amount of the
movement .DELTA.d in which the light beam source and the coupling
lens are integrally moved, and the amount of the change
.DELTA.m.sub.0 of the lateral magnification ratio of the objective
lens at that time, will be considered as follows.
The amount of the movement .DELTA.d of the light beam source and
the coupling lens can be expressed by the following equation,
Here, f.sub.0 is a focal length of the objective lens.
This equation is transformed as follows.
When this equation is substituted into Equation (45),
Therefore, the relationship among .DELTA.d, .DELTA.t and the
objective lens is obtained from Equation (44) as follows.
In order to simplify the equation, the left side of Equation (53)
is expressed as G. That is,
In order to suppress the spherical aberration generated
corresponding to the change .DELTA.t of the substrate thickness
within the Marechal criterion (the wavefront aberration of 0.07
.lambda.rms) by changing .DELTA.d, it is required to suppress the
spherical aberration within 0.045 .lambda.rms as the wavefront
aberration value when considering production errors or the like, as
the target value to be compensated for.
When .DELTA.d is set so that G exceeds the upper limit of -0.5, the
spherical aberration enters into the "under"-range, and the
spherical aberration exceeds 0.045 .lambda.rms even when NA2 is
about 0.3. When .DELTA.d is set so that G is reduced to less than
the lower limit of -2.1, the spherical aberration enters into the
overcorrected-range, and the spherical aberration exceeds 0.045
.lambda.rms even when NA2 is about 0.3.
When NA2 is increased to greater than 0.50, it is difficult to
maintain the spherical aberration within 0.045 .lambda.rms if G is
not exactly within the range from -1.5 to -0.8.
Specifically, when G is larger than -1.3 and smaller than -1.0, the
spherical aberration is close to 0, resulting in excellent
performance.
When NA1 is smaller than 0.5, it is not advisable to use the
coupling optical system, and when NA1 and NA2 exceed 0.65,
excellent performance can not be obtained.
In cases where the magnification ratio mt1 of a composite system of
the objective lens and the coupling lens when the transparent
substrate having the minimum thickness is used, is larger than
-0.095, it is not advisable to use the coupling optical system.
When mt1 is smaller than -0.22, the lateral magnification ratio
mt2, in cases where the transparent substrate is thick, is
increased further, and tends to be subject to the influence of
changes of temperature, or the like. Further, the influence of
distribution of the amount of the laser beams and the astigmatic
difference becomes greater, resulting in deterioration of the
performance.
Further, when mt1 is less than -0.12, the amount of a semiconductor
laser can be sufficiently utilized and it can be utilized as the
recording optical system.
When mt1 is lower than -0.17, and NA2 is greater than 0.5 at the
second arrangement position, the system tends to be subject to the
influence of changes of temperature, and the performance tends to
be deteriorated due to the influence of the distribution of the
amount of the semiconductor laser beam and astigmatic
differences.
When the lateral magnification m01 of the objective lens single
body at the first arrangement position, is greater than -0.06, the
distance from the light beam source to the information reording
medium is increased in order to maintain some working distance
between the objective lens and the surface of the substrate of the
information rcording medium. When it is corrected by the coupling
lens, the magnification ratio of the coupling lens is increased,
and it is difficult to maintain satisfactory performance.
The allowable range in which a variation of the spherical
aberration due to a change of distance from the laser beam source
to the information recording medium, due to unintentional movement
of the information recording medium, or the like, does not
influence over the performance, is more than -0.18.
Further, when the objective lens is made of resin material, the
allowable range in which not only a change of distance from the
laser beam source to the information recording medium, due to
unintentional movement of the information recording medium, or the
like, but also a change of the temperature does not influence over
the performance, is more than -0.13.
When the coupling lens is formed as a spherical single lens, the
lens is easily processed and its performance can be maintained at
low cost.
In cases where the objective lens related here is a high NA lens,
when the magnification ratio m.sub.c of the coupling lens, viewed
from the side opposite to the light beam source, is smaller than
0.48, its performance can not be maintained if the coupling lens is
a spherical single lens.
Further, when the magnification ratio m.sub.c is larger than 0.85,
it makes no sense to use a coupling lens in this optical
system.
An embodiment to attain the second object of the present invention
is accomplished by adopting any one of the following
structures.
(1) In an optical disk apparatus for reproducing information
signals from a plurality of types of optical disks, an optical
pick-up apparatus has a correction means to correct conditions of
an optical spot converged onto the information recording surface of
the optical disk corresponding to the type of the optical disk, and
the optical disk apparatus is characterized in that: the optical
pick-up devie is supported so that it can linearly move between a
position P.sub.IN inside the inner-most peripheral position in
which information in a lead-in area in an information track of the
optical disk can be read, and a position p.sub.out outside an
outer-most peripheral position in which information in a lead-out
area can be read; the correction means is driven by moving the
optical pick-up apparatus from the outer-most peripheral position,
in which information in the lead-out area can be read, to the
P.sub.out position, by a feed motor; the corrected condition of the
optical spot is determined as the first optical spot condition
corresponding to the first type of optical disk; the correction
means is driven by moving the optical pick-up from the inner-most
peripheral position, in which information in the lead-in area can
be read, to the P.sub.IN position by the motor; and the corrected
condition of the optical spot is determined as the second optical
spot condition corresponding to the second type of optical
disk.
(2) In an optical disk apparatus for reproducing information
signals from a plurality of types of optical disks, an optical
pick-up apparatus has a correction means to correct conditions of
the optical spot converged onto the information recording surface
of the optical disk corresponding to the type of the optical disk,
and the optical disk apparatus is characterized in that: the
optical pick-up apparatus is supported so that it can linearly move
between the lead-in area and the lead-out area including at least
one of the position P.sub.IN inside the inner-most peripheral
position in which information in the lead-in area in the
information track of the optical disk can be read, and the position
p.sub.out outside an outer-most peripheral position in which
information in a lead-out area can be read; and the correction
means is successively driven so that the condition of the optical
spot is corrected by moving the optical pick-up apparatus from the
inner-most peripheral position in which information in the lead-in
area can be read, to the P.sub.IN position, or from the outer-most
peripheral position in which information in the lead-out area can
be read, to the P.sub.OUT position, by the feed motor.
(3) In an optical disk apparatus having an optical pick-up
apparatus provided with a correction means for correcting the
condition of the optical spot which is converged onto the
information recording surface of the optical disk, corresponding to
types of optical disk, the optical disk apparatus has an optical
pick-up apparatus characterized in that: the correction means is
driven to correct the condition of the optical spot by a drive
means provided in a chassis portion when the optical pick-up
apparatus is located at a position in which information in the
lead-in area in the information track of the optical disk can be
read, or located on the side of the inner periphery of said
position.
(4) In an optical disk apparatus which is a means for correcting
the conditions of the optical spot when a correction means for
correcting the conditions of the optical spot which is converged
onto the information recording surface of the optical disk
corresponding to the types of optical disks, is moved linearly or
rotatably in the optical pick-up apparatus, the optical disk
apparatus has an optical pick-up apparatus characterized in that:
the optical pick-up apparatus is supported so that it can move in
the direction of the inner and outer periphery of the optical disk;
and the direction of linear movement or the direction of the
rotational axis of the rotational movement of the correction means
is different from the direction of the movement to the inner and
outer periphery.
(5) An optical disk apparatus having at least a correction means
for correcting the conditions of the optical spot converged onto
the information recording surface of the optical disk corresponding
to types of the optical disks, the objective lens and an objective
lens driving means in a movable portion which is linearly moved at
high speed to the direction of the inner and outer periphery of the
optical disk, the optical disk apparatus characterized in that: the
correction means is arranged so that the center of gravity of the
movable portion is not changed in a plane perpendicular to the
direction of linear movement even when corrected by the correction
means.
(6) The optical disk apparatus according to any of the apparatus
(1) to (5), having: a correction condition detection means for
detecting the condition of the correction means for correcting the
condition of the optical spot converged onto the information
recording surface of the optical disk corresponding to the types of
optical disks; and a read-in position detection means for detecting
that the optical pick-up apparatus positions lead-in areas of
plurality of types of optical disks in a commonly readable
position, the optical disk apparatus characterized in that a
focus-search operation is carried out after detecting that outputs
from the correction condition detection means and the read-in
position detection means respectively coincide with predetermined
values.
(7) The optical disk apparatus according to any of the apparatus
(1) to (6), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by insertion
and removal of a lens into the optical path and from the optical
path from the laser beam source to the objective lens.
(8) The optical disk apparatus according to any of the apparatus
(1) to (6), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by insertion
and removal of a parallel plane plate into and from the converging
luminous flux between the objective lens and the optical disk.
(9) The optical disk apparatus according to any of the apparatus
(1) to (6), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by movement of
the light beam source including the laser beam source in the
direction of the optical axis.
(10) The optical disk apparatus according to any of the apparatus
(1)m and (6), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by movement of
a divergence changing lens arranged in the optical path from the
laser beam source to the objective lens, in the direction of the
optical axis.
(11) The optical disk apparatus according to any of the apparatus
(1) to (6), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by selecting
one of a plurality of objective lenses by movement of an objective
lens driving means by which a plurality of objective lenses are
integrally driven.
(12) The optical disk apparatus according to any of the apparatus
(1) to (6), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by selecting
one of a plurality of objective lenses when at least, the laser
beam source, beam splitter or an optical detector is integrally
moved with respect to the objective lens driving means by which a
plurality of objective lenses are integrally driven.
(13) The optical disk apparatus according to any of apparatus (1)
to (6), wherein the correction means of the optical pick-up
apparatus, having an objective lens driving means for integrally
driving a plurality of objective lenses, and having a mirror to
bend the optical path by 90.degree. between the objective lens
driving means and the laser beam source, corrects the condition of
the optical spot by selecting the objective lens, into which the
laser beam enters, when the mirror is moved in the direction of the
optical axis of the laser beam.
(14) The optical disk apparatus according to any of apparatus (1)
to (13), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by adjusting
the aperture diameter of the luminous flux entering into the
objective lens.
(15) The optical disk apparatus according to any of apparatus (1)
to (14), wherein the correction means of the optical pick-up
apparatus corrects the condition of the optical spot by rotating
the azimuth angle of 3-beams with respect to the direction of the
track of the optical disk.
In the present invention, the correction means for correcting the
condition of the optical spot converged onto the information
recording surface of the optical disk corresponding to a plurality
of types of optical disks in which the thickness of the substrates
or the information recording density are different from each other,
is provided in the optical pick-up apparatus. Driving the
correction means is carried out by the driving force of the feed
motor of the optical pick-up apparatus, or by the drive means such
as a motor or solenoid provided on a chassis, which is provided
separately from the optical pick-up apparatus, without mounting the
driving means, such as a motor or a solenoid, on the optical
pick-up apparatus.
In this connection, the correction of the condition of the optical
spot is carried out using one or a plurality of the following
methods,
1. the aberration correction corresponding to the thickness of the
optical disks
2. the correction of the optical spot size corresponding to the
difference of the information recording density
3. rotation of an azimuth angle of 3-beams corresponding to the
difference of the track pitches.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing the optical path of an objective lens in
which the aberration correction is optimized.
FIG. 2 is a view showing the relationship between the thickness of
the substrate and the divergence degree when the objective lens
shown in FIG. 1 is used.
FIG. 3 is a view showing the case in which divergent light beams
enter into the objective lens when the thickness of the substrate
is increased.
FIG. 4 is a view showing the case in which convergent light beams
enter into the objective lens when the thickness of the substrate
is decreased.
FIG. 5 is a view corresponding to the case where the thickness of
the first substrate is 0.6 mm in Example 1.
FIG. 6 is a view corresponding to the case where the thickness of
the second substrate is 1.2 mm in Example 1.
FIG. 7 is a view corresponding to the case where the thickness of
the second substrate is 1.2 mm in Example 2.
FIG. 8 is a view of a 3-spot arrangement on the track (track pitch
0.75 mm).
FIG. 9 is another view of 3-spot arrangement on the track (track
pitch 1.6 mm).
FIG. 10 shows Example 3 in which the lens is moved in an optical
axis direction using a lens frame moving means having a circular
arc movement.
FIG. 11 is a view corresponding to the thickness of 1.2 mm of the
second substrate in Example 4.
FIG. 12 is a view corresponding to the thickness of 1.2 mm of the
second substrate in Example 5.
FIG. 13 is a view corresponding to the thickness of 0.8 mm of the
first substrate in Example 5.
FIG. 14 is a view corresponding to the thickness of 1.2 mm of the
second substrate in Example 6.
FIG. 15 is a view of an optical system in the arrangement in
Example 7.
FIG. 16 is a view of the optical system in the example which is
conventionally proposed.
FIG. 17 is a view showing the relationship between the thickness
error and wavefront aberration.
FIG. 18 is a graph showing the relationship between an amount of
movement of a divergence changing lens and spherical aberration in
Example 8 of the present invention.
FIGS. 19(a) and 19(b) are views of the optical path in cases in
which the thickness of the transparent substrates are respectively
0.6 mm and 1.2 mm in Example 8 of the present invention.
FIG. 20(a) is a view showing the spherical aberration in the case
in which the thickness of the transparent substrate is 0.6 mm in
the optical system in Example 8.
FIG. 20(b) is a view showing the spherical aberration of the
divergence changing lens in the case where the 1.2 mm thickness of
the transparent substrate is inserted while the 0.6 mm thickness of
the transparent substrate is arranged.
FIG. 20(c) is a view showing the spherical aberration of the
divergence changing lens in the case where the 0.6 mm thickness of
the transparent substrate is inserted while the 1.2 mm thickness of
the transparent substrate is arranged.
FIG. 20(d) is a view showing the spherical aberration in the case
where the optical system is adjusted for 1.2 mm thickness of the
transparent substrate.
FIGS. 21(a) and 21(b) are views of the optical path when the
thickness of the transparent substrates are respectively 0.6 mm and
1.2 mm in Example 9 of the present invention.
FIG. 22(a) is a view of the spherical aberration in the case of 0.6
mm thickness of transparent substrate in the optical system in
Example 9.
FIG. 22(b) is a view of the spherical aberration of the divergence
changing lens when 1.2 mm thickness of transparent substrate is
inserted while 0.6 mm thickness of transparent substrate is
arranged.
FIG. 22(c) is a view of the spherical aberration of the divergence
changing lens when 0.6 mm thickness of transparent substrate is
inserted while 1.2 mm thickness of transparent substrate is
arranged.
FIG. 22(d) is a view of the spherical aberration in the case where
the optical system is adjusted for 1.2 mm thickness of the
transparent substrate.
FIGS. 23(a) and 23(b) are views of the optical path in cases where
the thickness of the transparent substrates are respectively 0.6 mm
and 1.2 mm in Example 10 of the present invention.
FIG. 24(a) is a view of the spherical aberration in the case of 0.6
mm thickness of the transparent substrate in the optical system in
Example 10.
FIG. 24(b) is a view of the spherical aberration of the divergence
changing lens when 1.2 mm thickness of transparent substrate is
inserted while 0.6 mm thickness of transparent substrate is
arranged.
FIG. 24(c) is a view of the spherical aberration of the divergence
changing lens when 0.6 mm thickness of transparent substrate is
inserted while 1.2 mm thickness of transparent substrate is
arranged.
FIG. 24(d) is a view of the spherical aberration in the case where
the optical system is adjusted for 1.2 mm thickness of the
transparent substrate.
FIGS. 25(a) and 25(b) are views of the optical path in cases where
the thickness of the transparent substrates are respectively 0.6 mm
and 1.2 mm in Example 11 of the present invention.
FIG. 26(a) is a view of the spherical aberration in the case of 0.6
mm thickness of transparent substrate in the optical system in
Example 11.
FIG. 26(b) is a view of the spherical aberration of the divergence
changing lens when 1.2 mm thickness of transparent substrate is
inserted while 0.6 mm thickness of transparent substrate is
arranged.
FIG. 26(c) is a view of the spherical aberration of the divergence
changing lens when 0.6 mm thickness of transparent substrate is
inserted while 1.2 mm thickness of transparent substrate is
arranged.
FIG. 26(d) is a view of the spherical aberration in the case where
the optical system is adjusted for 1.2 mm thickness of the
transparent substrate.
FIG. 27 is a view corresponding to the thickness of 0.6 mm of the
first substrate in Example 12.
FIG. 28 is a view corresponding to the thickness of 1.2 mm of the
second substrate in Example 12.
FIG. 29 is a view of an optical system in the arrangement in
Example 13.
FIGS. 30(a) and 30(b) are views of the optical path respectively
showing the first and second arrangement positions in Example 14 of
the present invention.
FIGS. 31(a), 31(b) and 31(c) are views of the spherical aberration
in Example 14 of the present invention.
FIG. 32 is a view showing changes of the wavefront aberration when
the thickness of the substrate is changed from 0.6 mm to 1.2 mm in
Example 14.
FIGS. 33(a) and 33(b) are views of the optical path respectively
showing the first and second arrangement positions in Example 15 of
the present invention.
FIGS. 34(a), 34(b) and 34(c) are views of the spherical aberration
in Example 15 of the present invention.
FIG. 35 is a view showing changes of the wavefront aberration when
the thickness of the substrate is changed from 0.6 mm to 1.2 mm in
Example 15.
FIGS. 36(a) and 36(b) are views of the optical path respectively
showing the first and second arrangement positions in Example 16 of
the present invention.
FIGS. 37(a), 37(b) and 37(c) are views of the spherical aberration
in Example 16 of the present invention.
FIG. 38 is a view showing changes of the wavefront aberration when
the thickness of the substrate is changed from 0.6 mm to 1.2 mm in
Example 16.
FIGS. 39(a) and 39(b) are views of the optical path respectively
showing the first and second arrangement positions in Example 17 of
the present invention.
FIGS. 40(a), 40(b) and 40(c) are views of the spherical aberration
in Example 17 of the present invention.
FIG. 41 is a view showing changes of the wavefront aberration when
the thickness of the substrate is changed from 0.6 mm to 1.2 mm in
Example 17.
FIGS. 42(a) and 42(b) are views of the optical path when the
thickness of the transparent substrates are 0.6 mm and 1.2 mm in
Example 18 of the information recording and reproducing optical
systems of the present invention.
FIGS. 43(a), 43(b) and 43(c) are views of the spherical aberration
in the optical system in Example 18. FIG. 43(a) is a view of the
spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 43(b) is a view of the spherical
aberration when 1.2 mm thickness of the transparent substrate is
inserted while 0.6 mm thickness of the transparent substrate is
arranged. FIG. 43(c) is a view of the spherical aberration when the
optical system is adjusted for 1.2 mm thickness of the transparent
substrate.
FIG. 44 is a graph showing changes of the wavefront aberration
while 0.6 mm thickness of the transparent substrate is adjusted to
1.2 mm thickness of the transparent substrate in Example 18.
FIGS. 45(a) and 45(b) are views of the optical path when the
thickness of the transparent substrates are 0.6 mm and 1.2 mm in
Example 19 of the present invention.
FIGS. 46(a), 46(b) and 46(c) are views of the spherical aberration
in the optical system in Example 19. FIG. 46(a) is a view of the
spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 46(b) is a view of the spherical
aberration when 1.2 mm thickness of the transparent substrate is
inserted while 0.6 mm thickness of the transparent substrate is
arranged. FIG. 46(c) is a view of the spherical aberration when the
optical system is adjusted for 1.2 mm thickness of the transparent
substrate.
FIG. 47 is a graph showing changes of the wavefront aberration
while 0.6 mm thickness of the transparent substrate is adjusted to
1.2 mm thickness of the transparent substrate in Example 19.
FIGS. 48(a) and 48(b) are views of the optical path when the
thickness of the transparent substrates are 0.6 mm and 1.2 mm in
Example 20 of the information recording and reproducing optical
systems of the present invention.
FIGS. 49(a), 49(b) and 49(c) are views of the spherical aberration
in the optical system in Example 20. FIG. 49(a) is a view of the
spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 49(b) is a view of the spherical
aberration when 1.2 mm thickness of the transparent substrate is
inserted while 0.6 mm thickness of the transparent substrate is
arranged. FIG. 49(c) is a view of the spherical aberration when the
optical system is adjusted for 1.2 mm thickness of the transparent
substrate.
FIG. 50 is a graph showing changes of the wavefront aberration
while 0.6 mm thickness of the transparent substrate is adjusted to
1.2 mm thickness of the transparent substrate in Example 20.
FIGS. 51(a) and 51(b) are views of the optical path when the
thickness of the transparent substrates are 0.6 mm and 1.2 mm in
Example 21 of the present invention.
FIGS. 52(a), 52(b) and 52(c) are views showing the spherical
aberration in the optical system in Example 21. FIG. 52(a) shows
the spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 52(b) shows the spherical aberration when
the transparent substrate of 1.2 mm thickness is inserted while the
transparent substrate of 0.6 mm thickness is arranged. FIG. 52(c)
shows the spherical aberration when the thickness of the
transparent substrate is adjusted to 1.2 mm.
FIG. 53 is a graph showing the change of the wavefront aberration
while the thickness of the transparent substrate is adjusted from
0.6 mm to 1.2 mm in Example 21.
FIGS. 54(a) and 54(b) are views showing the optical path when the
thickness of the transparent substrates is respectively 0.6 mm and
1.2 mm in Example 22 of the present invention.
FIGS. 55(a) 55(b) and 55(c) are views showing the spherical
aberration in the optical system in Example 22. FIG. 55(a) shows
the spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 55(b) shows the spherical aberration when
the transparent substrate of 1.2 mm thickness is inserted while the
transparent substrate of 0.6 mm thickness is arranged. FIG. 55(c)
shows the spherical aberration when the thickness of the
transparent substrate is adjusted to 1.2 mm.
FIG. 56 is a graph showing the change of the wavefront aberration
while the thickness of the transparent substrate is adjusted from
0.6 mm to 1.2 mm in Example 22.
FIGS. 57(a) and 57(b) are views showing the optical path when the
thickness of the transparent substrates is respectively 0.6 mm and
1.2 mm in Example 23 of the present invention.
FIGS. 58(a), 58(b) and 58(c) are views showing the spherical
aberration in the optical system in Example 23. FIG. 58(a) shows
the spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 58(b) shows the spherical aberration when
the transparent substrate of 1.2 mm thickness is inserted while the
transparent substrate of 0.6 mm thickness is arranged. FIG. 58(c)
shows the spherical aberration when the thickness of the
transparent substrate is adjusted to 1.2 mm.
FIG. 59 is a graph showing a change of the wavefront aberration
while the thickness of the transparent substrate is adjusted from
0.6 mm to 1.2 mm in Example 23.
FIGS. 60(a) and 60(b) are views showing the optical path when the
thickness of the transparent substrates is respectively 0.6 mm and
1.2 mm in Example 24 of the present invention.
FIGS. 61(a), 61(b) and 61(c) are views showing the spherical
aberration in the optical system in Example 24. FIG. 61(a) shows
the spherical aberration when the thickness of the transparent
substrate is 0.6 mm. FIG. 61(b) shows the spherical aberration when
the transparent substrate of 1.2 mm thickness is inserted while the
transparent substrate of 0.6 mm thickness is arranged. FIG. 61(c)
shows the spherical aberration when the thickness of the
transparent substrate is adjusted to 1.2 mm.
FIG. 62 is a graph showing a change of the wavefront aberration
while the thickness of the transparent substrate is adjusted from
0.6 mm to 1.2 mm in Example 24.
FIG. 63 is a view to explain the shape of the optical disk.
FIG. 64 is a view to explain the correction means in Example
25.
FIG. 65 is a view to explain the case where the optical pick-up is
moved to P.sub.IN in Example 25.
FIG. 66 is a view to explain the case where the optical pick-up is
moved to P.sub.OUT in Example 25.
FIG. 67 is a view to explain the correction means in Example
26.
FIG. 68 is a view to explain a correction mechanism in Example
26.
FIGS. 69(a) and 69(b) are views to explain correction mechanisms in
Example 26.
FIG. 70 is a view to explain a correction mechanism in Example
27.
FIG. 71 is a view to explain a correction mechanism in Example
28.
FIG. 72 is a view to explain a correction means in Example 29.
FIG. 73 is a view to explain a correction means in Example 30.
FIG. 74 is a view to explain a correction means in Example 31.
FIG. 75 is a view to explain a correction mechanism in Example
31.
FIG. 76 is a view to explain a correction means in Example 32.
FIG. 77 is a view to explain a correction means in Example 33.
FIG. 78 is a view to explain a correction means in Example 34.
FIG. 79 is a view to explain a correction means in Example 35.
FIGS. 80(a) and 80(b) are views to explain details of the
correction means in Example 35.
FIGS. 81(a) and 81(b) are views to explain the track error
detection in Example 36.
FIGS. 82(a) and 82(b) are views to explain the diffraction grating
in Example 36.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
1. Examples (1-11) relating to the first and second embodiments to
attain the first object will be described below.
Each example (1-11) includes the following numerical values. A
laser beam source is defined as the zero-th surface, and the radius
of curvature of the i-th surface, (including a diaphragm surface),
counted from the zero-th surface in order, is expressed by ri, an
interval between the i-th surface and the (i+1)-th surface is
expressed by di, and a refractive index of a medium between the
i-th surface and the i+1-th surface in the wavelength of a luminous
flux of the laser beam source is expressed by ni. The refractive
index of air is defined as 1.
In the case where an aspherical surface is used for a lens surface,
the shape of the aspherical surface is expressed by the following
equation when the conical coefficient is k, the aspherical surface
coefficient is Ai, and the numerical exponent of the aspherical
surface is Pi in an orthogonal coordinate system in which the
vertex of the surface is the origin, and the direction of the
optical axis is defined as the X-axis. ##EQU2##
EXAMPLE 1
FIG. 5 shows the structure of this system when an optical
information recording medium of the first substrate thickness of
0.6 mm is read.
The luminous flux emitted from a laser beam source 1 passes through
a hologram beam splitter 2, further passes through a lens 3 held by
a frame 20 which is movable in the direction of the optical axis,
and becomes almost a parallel luminous flux. The flux is limited to
a predetermined luminous flux by a diaphragm 5, and enters into an
objective lens 6. The luminous flux entered into the objective lens
6 is converged by the objective lens 6 onto a information recording
surface 8 through a substrate 7. The luminous flux, modulated by an
information pit located on the information recording surface 8 and
reflected on the information recording surface 8, returns to the
hologram beam splitter 2 after passing through the objective lens 6
and the lens 3, and is separated from the optical path of the laser
beam source 1, and then, enters into a light receiving means 9. The
light receiving means 9 is composed of multi-divided PIN
photodiodes, and a current proportional to the strength of the
entered luminous flux, flows from each element. This current is
sent to a detection circuit system, not shown in the drawing, and
an information signal, a focus error signal, and a track error
signal are generated in this detection circuit system. A
2-dimensional actuator (not shown in the drawings) composed of a
magnetic circuit and coils, or the like, controls the objective
lens 6 and the diaphragm 5 which are integrally provided with each
other, according to the focus error signal and the track error
signal, so that the optical spot position always coincides with the
information track.
An example of numerical values in the example shown in FIG. 5 is
shown below.
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3.0
1.514546 2 .infin. 23.9 1 3 -156 1.2 1.878333 4 -20.58 2.9 1 5
Diaphragm .infin. 0 1 (.phi.3.99) 6 2.0282 2.6 1.4981 7 -5.223
1.526 1 8 .infin. 0.6 1.58 9 Information recording surface
______________________________________ Aspherical coefficient of i
= 6 .kappa. = -0.54772 A.sub.1 = 5.0718 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = 3.2560 .times. 10.sup.-5 P.sub.2 = 6.0000 A.sub.3
= -6.0919 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 = -1.6366
.times. 10.sup.-6 P.sub.4 = 10.0000
______________________________________ Aspherical coefficient of i
= 7 .kappa. = -21.8737 A.sub.1 = 9.8897 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -2.9123 .times. 10.sup.-3 P.sub.2 = 6.0000 A.sub.3
= 5.7052 .times. 10.sup.-4 P.sub.3 = 8.0000 A.sub.4 = -5.0245
.times. 10.sup.-5 P.sub.4 = 10.0000
______________________________________
In this example, a divergent degree of the luminous flux entered
into the objective lens 6 corresponds to a little convergent light,
the wavefront aberration on the axis is 0.001 .lambda.rms at 0.6
NA, and 0.006 .lambda.rms, on the information recording surface
side, when the objective lens is shifted by 0.1 mm by tracking. The
reason for a little convergent light is to eliminate the spherical
aberration generated by the lens 3, by the objective lens.
A total magnification ratio of the lens 3 and the objective lens 6
between the laser beam source 1 and the information recording
surface 8 is -0.123, and NA on the side of the laser beam source is
0.074. Herein, the NA on the laser beam source side means an
effective NA actually guided to the optical information recording
medium, in the luminous flux emitted from the laser beam source,
and it is obtained by the following equation:
A semiconductor laser having a wave length of 635 nm is used as the
laser beam source 1, and the divergent light of the semiconductor
laser forms oval-shaped light beams of about 7.degree., and
30.degree. in the full width half maximum. In this example, as
described above, NA on the side of the laser beam source is 0.074,
and the luminous flux corresponding to a divergent angle of 4.3 at
the central portion is used. Accordingly, it can be considered that
the intensity is almost uniform.
Generally, the semiconductor laser has the astigmatism of about 5
to 10 .mu.m, however, in this example, since the magnification
ratio is -0.123, the astigmatism is a sufficiently small value of
about 0.08 to 0.15 .mu.m on the information recording surface, so
that the astigmatism can be neglected.
Next, when a 1.2 mm optical information recording medium, which is
thicker than the first recording medium, is read, the lens 3, which
is a divergence changing means, is moved to the second position on
the side of the laser beam source in the direction of the optical
axis by a moving means 21. Simultaneously, in order to adjust NA of
the luminous flux entering into the optical information recording
medium, the second diaphragm means 4 is inserted into the optical
path by a control means 22.
The structure in the above case is shown in FIG. 6.
A numerical example in the example shown in FIG. 6 is as
follows.
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3.0
1.514546 2 .infin. 14 1 3 -156 1.2 1.878333 4 -20.58 10.99 1 5
Diaphragm .infin. 2.0 1 (.phi.3.51) 6 2.0282 2.6 1.4981 7 -5.223571
1.341 1 8 .infin. 1.2 1.58 9 Information recording surface
______________________________________
Aspherical coefficients of i=6 and i=7 have the same value as that
of the example shown in FIG. 5.
The magnification of the total lenses of the lens 3 and the
objective lens 6 is -0.16 between the laser beam source 1 and the
recording surface 8, the NA on the side of the information
recording surface is 0.52, and the NA on the side of the light beam
source is 0.083. The wavefront aberration on the axis is 0.003
.lambda.rms, and 0.016 .lambda.rms when the objective lens is
shifted by 0.1 mm by tracking. In this connection, the second
diaphragm means 4 is not moved during tracking of the objective
lens.
As described above, when the lens 3 is moved in the direction of
the optical axis of the luminous flux of the laser beam source, the
spherical aberration due to the difference of the thickness of the
substrate can be canceled by changing the divergence degree of the
luminous flux entering into the objective lens, and information of
the optical information recording medium having a different
substrate thickness can be read.
When the lens system corresponds to only two types of substrate
thickness (for example, 0.6 mm, and 1.2 mm), the moving means 21
may mechanically push a frame holding the lens 3 to two points for
fixing, by using a motor and a solenoid, resulting in a simple
structure.
When the lens system corresponds to more than 3 types of substrate
thickness, a position sensor to detect a position of the lens 3 is
provided and the moving means 21 may be controlled by the output
from this sensor.
Further, a control means 22 to attach or detach the diaphragm means
4 can be interlocked with the moving means 21, and its overall
dimensions can be reduced when it is driven by a motor or a
solenoid.
Further, fluctuation of the thickness of the substrates can also be
corrected when the lens position 3 is minutely adjusted by the
moving means 21.
When the thickness of the substrate is not 0.6 mm, but 0.57 mm or
0.63 mm at 0.60 NA on the side of the recording surface, the
aberration of 0.03 .lambda.rms is respectively generated. In the
case of a 0.57 mm substrate thickness, when the lens 3 is moved to
the side of the objective lens by 0.9 mm so that the converging
light is entered further into the objective lens 6, the aberration
is corrected to 0.001 .lambda.rms. When the thickness of the
substrates 0.63 mm, the lens 3 is moved to the side of the laser
beam source by 0.85 mm so that the divergent light is entered into
the objective lens 6, and the aberration can be corrected to 0.001
.lambda.rms.
Further, by this method, the aberration of each surface of the
optical information recording medium, having a plurality of
information recording surfaces in the direction of the thickness,
can be corrected most appropriately.
For example, when there are 2 more information recording layers at
0.03 mm intervals in the direction of the thickness in the 0.57 mm
thickness substrate, aberration correction corresponding to
0.6.+-.0.03 mm may be carried out, and in this case, the movement
of lens 3 of the same amount as in the case of the error correction
of .+-.0.03 mm may be carried out.
In order to correct the fluctuation of the substrate thickness,
after at least a focusing-servo operation is applied on the
information recording surface 8 of the optical information
recording medium, the position of the lens 3 is moved so that the
amplitude of the reproduced signal becomes larger, or jittering
becomes smaller. When the above operation is carried out during
information reproducing, or during waiting under the condition that
at least the focusing-servo operation is applied, then, generation
of spherical aberration due to temperature and humidity in the
information pick-up system or the optical information recording
medium, can be corrected.
In this example, when the thickness of the substrate is 0.6 mm, the
objective lens 6, in which the aberration is corrected by incidence
of the parallel light, is used. When the thickness of the substrate
is 1.2 mm, the objective lens 6, in which the aberration is
corrected by incidence of the parallel light, is used, and as the
lens which is the divergence changing means, a lens through which a
parallel luminous flux is emitted at the first lens position
separated from the objective lens, is used. When the converging
luminous flux is emitted through the lens at the second position
near the objective lens, this lens system can also correspond to
two or more types of substrate thickness.
Alternatively, for example, a lens, the aberration of which is
corrected by incidence of the parallel light in the case of the 0.8
mm substrate thickness, is used as the objective lens. In the case
of 0.6 mm thickness, the converging light may be emitted through
the lens, which is the divergence changing means, at the second
position near the objective lens 6, and in the case of 1.2 mm
thickness, the divergent light may be emitted through the lens,
which is the divergence changing means, at the first position
separated from the objective lens 6.
In this connection, it is preferable that the spherical aberration,
generated depending on the substrate thickness, is eliminated so
that the optical spot has no aberration, and that the optical spot
has a size which is most appropriate depending on the types of the
information recording surface of the optical information recording
medium. The optical spot size is mainly determined depending on NA
on the light emergent side of the objective lens, and the
wavelength. In the case where information is read from the
information recording surface in which a pit-string is recorded in
the shape of track, when NA is too larger with respect to the
pit-string, and the optical spot size is too small, the tilt error,
thickness error, polarization dependency, and a symmetry of
eye-pattern, of the substrate, become larger. Accordingly, a
diaphragm diameter changing means to determine the optical spot
size depending on the difference of types, specifically, depending
on the difference of recording density represented by the track
pitch, is prepared. When the diaphragm diameter is reduced, and NA
is reduced, the optical spot size becomes larger. For example, the
diaphragm diameter is reduced so that: .lambda./NA=approximately
1.75 (.mu.m) in the case of the medium of the CD standard, and NA
on the side of the information recording surface is approximately
0.36 when .lambda.=635 nm. When the diaphragm diameter is reduced
as described above, the aberration generated at the time of
focusing and tracking of the objective lens, and the accuracy of
lens setting by which the lens which is the divergence changing
means is positioned at the second position separated from the
objective lens, can be reduced.
When parallelism between the objective lens and the substrate
deviates due to warping or waviness of the substrate, or an
assemble error of the information pick-up apparatus, etc., coma is
generated. The larger NA on the side of the information recording
surface is, or the larger the substrate thickness is, the larger
the coma is. When the coma is generated, the first ring of the
optical spot becomes asymmetric, resulting in deterioration of the
reproduction signal. Accordingly, when the divergence degree of the
luminous flux entering into the objective lens 6 is changed and the
lens system corresponds to the thicker substrate, it is preferable
that NA of the luminous flux entering into the information
recording surface is reduced. Although NA 0.6 is reduced to 0.52 in
the example, NA on the side of the information recording surface
can be reduced by a single diaphragm means when the thickness of
the substrate is large, and the divergence degree of the luminous
flux entering into the objective lens is large, by setting a
diaphragm, movable at the time of focusing and tracking, on the
side of the information recording medium separated from a focal
position on the side of incidence of the luminous flux into the
objective lens, integrally with the objective lens. The nearer the
diaphragm means to the surface of the information recording medium,
the larger the effect is. Therefeore, the diaphragm means is
preferably provided on the side of emission of the light of the
objective lens.
In the example shown in FIG. 6, when the substrate is inclined by
0.3.degree., the front wave aberration is reduced to 0.04
.lambda.rms. This is almost coma. In this connection, in this
structure, non-parallel light is entered into the objective lens 6,
and when the objective lens 6 is shifted by tracking, coma is
generated. Accordingly, when the optical information recording
medium is inclined by warping or the like, the coma can be canceled
when the objective lens 6 is shifted. In the case where the
substrate is inclined by 0.3.degree., the wavefront aberration of
0.04 .lambda.rms can be reduced to 0.009 .lambda.rms, when a DC
bias current is applied on a tracking actuator and the objective
lens 6 is shifted by 0.22 mm.
EXAMPLE 2
The information pick-up apparatus using a moving means, in which a
lens frame rotating means 211 for reversing and moving the lens 3
between the beam splitter 2 and the objective lens 6 is used, is
shown in FIG. 7 as the information pick-up apparatus to reproduce
two types of optical information recording medium in which a 0.6 mm
substrate is used as the substrate of the first thickness, and a
1.2 mm substrate is used as the thicker substrate of the second
thickness. FIG. 7 shows the optical system in which the laser beam
source 1, beam splitter 2, lens 3, objective lens 6, the optical
detector as the light receiving means 9, which are the same as
those in Example 1, are used, and when the information on the
information recording surface of the 0.6 mm substrate is read, the
positional arrangement of the optical system is the same as that in
FIG. 5 in Example 1. The aberration is 0.001 .lambda.rms on the
axis, and when the objective lens is shifted by 0.1 mm by tracking,
the aberration is 0.006 .lambda.rms.
FIG. 7 shows the structure of the optical system when the
information recording surface of 1.2 mm thickness substrate is
reproduced.
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3.0
1.514546 2 .infin. 15.4 1 3 20.58 1.2 1.878333 4 156 9.6 1 5
Diaphragm 2 1 (.phi.2.43) 6 2.0282 2.6 1.4981 7 -5.2236 1.328 1 8
.infin. 1.2 1.58 9 Information recording surface
______________________________________
The aspherical surface coefficients of i=6 and i=7 are the same as
those in Example 1.
In this structure,
NA on the side of the information recording surface is 0.36;
NA on the side of the laser beam source is 0.057;
the magnification ratio between the laser beam source and the
information recording surface is -0.158;
the wavefront aberration on the axis is 0.001 .lambda.rms; and
the wavefront aberration at the time of 0.1 mm shift of the
objective lens is 0.006 .lambda.rms.
When the lens 3 is reversed, an under-spherical aberration is
generated by the lens 3, and the effect of correction of the
overcorrected-spherical aberration due to an increase of the
substrate thickness is increased. The lens 3 is held in a lens
holding frame 201, and when it is rotated around an axis 31 which
is perpendicular to the optical axis, the first position and the
second position are switched. For this switching operation, a motor
or a solenoid can be used.
When the motor is used, the lens 3 is moved to the first position
(or the second position), and an amount of rotation of the lens
holding frame 201 is minutely adjusted. Thereby, the coma generated
by the inclination of the substrate can be eliminated. In this
case, the direction of the rotation axis 31 is set so that the lens
holding frame can be minutely adjusted by the rotation of the lens
3 in the direction in which the inclination of the substrate tends
to occur.
In this example, NA on the side of the laser beam source is 0.074
in the case of the 0.6 mm thickness substrate, and NA on the side
of the laser beam source is 0.057 in the case of the 1.2 mm
thickness substrate. In this case, the utilization factor of the
laser beam is about 1:0.59. Accordingly, light intensity detected
by the light detector is also 1:0.59, and each signal intensity is
lowered when using the 1.2 mm thickness substrate. Accordingly,
when the divergent degree of the laser beam is switched to that
used at the time of 1.2 mm thickness substrate, it is preferable
that the amount of the laser beam is simultaneously increased by
approximately 70%, or a gain of the processing system for detecting
the current outputted from the light detector is increased by
approximately 70%.
Reversely, when the NA on the side of the information recording
surface is about 0.47 corresponding to the 1.2 mm thickness
substrate, the NA on the side of the laser beam source is 0.074.
Accordingly, even when the thickness of the substrate is different,
the utilization factor of the laser beam is almost equal, so that
adjstment of the amount of the laser beam, and the structure of the
signal processing system become simple.
Further, a diaphragm 202 can be integrally provided with the lens
holding frame 201 at a portion distant from the lens 3 on the lens
holding frame 201, resulting in a simpler structure.
When a 3-beam method is used for detecting the deviation
(track-error) between the information track and the optical spot on
the information recording surface, a diffraction grating is
arranged in the optical path between the laser beam source and the
beam splitter, and .+-.1-order light diffracted by the grating is
converged onto the information recording surface as the optical
spot which is shifted by a 1/4 track from the center of the
information track. This reflected light is received by the light
detector, and is detected as a tracking error signal.
In this example, when the track pitch on the information recording
surface of the optical information recording medium having a 0.6 mm
substrate thickness is 0.75 .mu.m, and spot intervals among
.+-.1-order light spots and the reading spot due to the 0-order
light are 20 .mu.m, and when an angle, formed by a line connecting
these three spots and the information track, is 0.54.degree., then,
the deviation is 1/4 track (FIG. 8).
In this case, when the lens 3 is rotated at the 1.2 mm substrate
thickness, the magnification ratio between the laser beam source
and the information recording surface is changed from -0.123 to
-0.158, and the spot intervals between the .+-.1-order light spots
and the reading spot are 15.6 .mu.m. In this case, when the track
pitch of the information track on the information recording surface
is 1.6 .mu.m, it is preferable that the angle formed by a line
connecting these 3 spots and the information track is 1.47.degree.
(FIG. 9).
Accordingly, it is preferable that the divergent angle is changed
corresponding to the substrate thickness, and the angle formed
between the line connecting 3 spots on the information recording
surface and the information track, is changed corresponding to the
pitch of the information track.
This can be realized by the following methods: only diffraction
grating is integrally held and rotated; the laser beam source,
diffraction grating, beam splitter, and light detector are
integrally rotated around the optical axis extending to the
objective lens; or the entire information pick-up apparatus is
rotated with respect to the optical information recording
medium.
A light beam projecting and receiving unit is integrally provided
with the laser beam source, beam splitter and light beam detector,
and when the light beam projecting and receiving unit is moved in
the direction of the optical axis in the same manner as in Example
12, which will be described later, the range of the thickness of
the substrate by which the spherical aberration can be corrected,
is more enlarged. Further, when the mechanism is simplified and the
light beam projecting and receiving unit is moved by the 2-point
switching method, this system can correspond to 4-thicknesses of
the substrate in combination with 2-point rotational movement of
the divergence changing lens.
EXAMPLE 3
As Example 3, an optical pick-up apparatus, in which a lens frame
moving means 231, for circularly moving the lens 3 between the beam
splitter 2 and the objective lens 6 as a moving means, is used, is
shown in FIG. 10 as an optical pick-up apparatus to redproduce 2
types of optical information recording mediums, respectively having
a first substrate thickness of 0.6 mm and a second substrate
thickness of 1.2 mm, which is thicker than the first substrate
thickness. A laser beam source 1, beam splitter 2, lens 3, lens 6,
and light receiving means 9, etc., are the same as those in Example
1. A diaphragm means 5 to determine NA on the side of the
information recording surface, is provided on the side of emission
of the objective lens 6, and can be moved at focusing and tracking
integrally with the objective lens. A lens frame 230 is supported
by the optical pick-up main body using 2-parallel links so as to
rotate around the axis perpendicular to the optical axis. Because
parallel links are used, even when the lens frame is rotated, the
lens 3 can maintain its perpendicularity with respect to the
optical axis connecting the laser beam source 1 to the objective
lens.
In the arrangement shown by a solid line in the drawing, the
luminous flux diversed from the laser beam source 1, is formed into
parallel luminous flux through the lens 3 which is the divergence
changing means, and enters into the objective lens 6. Then, the
diameter of the luminous flux is reduced to a predetermined NA by
the diaphragm means 5, and converged onto the information recording
surface 8 as an almost non-aberration optical spot through the
substrate 7 having the first substrate thickness of 0.6 mm.
The number of the link may be one when the lens frame is contacted
with the side of the optical pick-up apparatus main body, and the
perpendicularity of the lens 3 with respect to the optical axis can
be maintained by being pushed by a spring.
The reason for the diaphragm means 5 being arranged at the side of
emission of the objective lens 6, is as follows. When the lens 3 is
positioned at a position corresponding to the 1.2 mm substrate
thickness as shown by a dotted line, and diverging light beams are
entered into the objective lens 6, NA on the side of the
information recording surface is reduced further. When NA is
reduced, generation of the coma due to inclination of the substrate
can be suppressed. The diaphragm means 5 is set close to the
substrate within the range in which the required operation distance
from the substrate surface can be obtaibed. In order to prevent
damage onto the substrate, a self-lubrication property is
preferably provied on the side of information recording medium of
the diaphragm means 5.
EXAMPLE 4
In this example, the optical system in Example 1 is used and the
optical information recording medium of the 0.6 mm thickness
substrate is reproduced. When the substrate thickness is 1.2 mm, an
optical element 401 having a concave lens function by which the
divergent degree is increased, is inserted into the optical path
from the laser beam source to the objective lens.
The structure at the 1.2 mm thickness substrate is shown in FIG.
11.
The structure of the optical system is as follows.
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3 1 2
.infin. 21.9 1 3 -10.2174 1 1.4981 4 -23.0258 1 1 5 -156 1.2
1.878333 6 -20.58 3.06 1 7 2.0282 2.6 1.4981 8 -5.2236 1.367 1 9
.infin. 1.2 1.58 10 Information recording surface
______________________________________ Aspherical coefficient of i
= 4 .kappa. = 14.94238 A.sub.1 = 1.6539 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = 6.9517 .times. 10.sup.-4 P.sub.2 = 6.0000 A.sub.3
= 8.2519 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 = -4.6438
.times. 10.sup.-6 P.sub.4 = 10.0000
______________________________________
Aspherical surface coefficients of i=7 and i=8 are the same as
those in Example 1.
NA on the information recording surface-side 0.55
NA on the laser beam source-side 0.064
Magnification ratio between the information recording surface and
the laser beam source -0.116
Wavefront aberration on the axis 0.001 .lambda.rms
Wavefront aberration in the case of 0.1 mm shift of the objective
lens 0.007 .lambda.rms
In this example, although this optical element 401 is inserted
between the beam splitter and the lens 3, it maybe inserted between
the lens 3 and the objective lens 6. In this structure, NA on the
laser beam source-side is easily increased, and the utilization
efficiency of the luminous flux is higher.
EXAMPLE 5
In this example, the objective lens 6 is used by which laser beams
diverging from a finite distance are directly converged through the
1.2 mm thickness substrate without aberration. Specifically, in
this example, the 1.2 mm thickness substrate is used which
corresponds to densification and is excellent in reproduction using
small optical spots.
In FIG. 12,
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3
1.514546 2 .infin. 17 1 3 Diaphragm .infin. 2 1 4 1.9095 2.7 1.4981
5 -2.9131 1.162 1 6 .infin. 1.2 1.58 7 Information recording
surface ______________________________________ Aspherical
coefficient of i = 4 .kappa. = -1.75740 A.sub.1 = 1.8932 .times.
10.sup.-2 P.sub.1 = 4.0000 A.sub.2 = -1.2233 .times. 10.sup.-3
P.sub.2 = 6.0000 A.sub.3 = 1.8861 .times. 10.sup.-4 P.sub.3 =
8.0000 A.sub.4 = -9.3147 .times. 10.sup.-6 P.sub.4 = 10.0000
______________________________________ Aspherical coefficient of i
= 5 .kappa. = -9.20981 A.sub.1 = 6.1162 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -1.5274 .times. 10.sup.-4 P.sub.2 = 6.0000 A.sub.3
= -1.4276 .times. 10.sup.-4 P.sub.3 = 8.0000 A.sub.4 = 1.7874
.times. 10.sup.-5 P.sub.4 = 10.0000
______________________________________
NA on the information recording surface-side 0.55
NA on the laser beam source-side 0.080
Magnification ratio between the information recording surface and
the laser beam source -0.145
Wavefront aberration on the axis 0.000 .lambda.rms
Wavefront aberration in the case of 0.1 mm shift of the objective
lens 0.001 .lambda.rms
In FIG. 13, a lens 501 having a convex lens function, with which a
diaphragm 502 is integrally held in a holding frame, is inserted
between the beam splitter 2 and the objective lens 6 in order to
correspond to the 0.8 mm thickness substrate.
The diaphragm 503 is also integrally provided in the holding frame
at the 1.2 mm thickness substrate.
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3
1.514546 2 .infin. 16.2 1 3 -2.9942 1.3 1.4981 4 -3.0208 1.5 1 5
1.9095 2.7 1.4981 6 -2.9131 1.162 1 7 .infin. 0.8 1.58 8
Information recording surface
______________________________________ Aspherical coefficient of i
= 4 .kappa. = 0.03174 A.sub.1 = 8.2371 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = 2.1896 .times. 10.sup.-4 P.sub.2 = 6.0000 A.sub.3
= -4.7237 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 = 1.1840
.times. 10.sup.-5 P.sub.4 = 10.0000 A.sub.5 = -2.1310 .times.
10.sup.-6 P.sub.5 = 12.0000
______________________________________
NA on the information recording surface-side 0.55
NA on the laser beam source-side 0.071
Magnification ratio between the information recording surface and
the laser beam source -0.129
Wavefront aberration on the axis 0.002 .lambda.rms
Wavefront aberration in the case of 0.1 mm shift of the objective
lens 0.017 .lambda.rms
The diaphragm to determine NA on the information recording
surface-side is also provided on the fourth surface.
In this example, the distance from the light emerging surface of
the objective lens 6 to the substrate surface is the same, and the
movable range, in the direction of focusing, of an actuator to
drive the objective lens can be reduced, resulting in a decrease of
the overall actuator size.
Also in this example, the aberration generated when the objective
lens 6 is shifted, is mainly coma, and the coma due to the
inclination of the substrate can be canceled when a bias current is
applied onto the tracking actuator or the lens 501 to be inserted,
is shifted by a motor.
EXAMPLE 6
In Example 6, one of a plurality of lenses having different
refractive power is selectively inserted as shown in FIG. 14, so
that the divergent degree of the luminous flux entering into the
objective lens 6 can be adjusted.
The optical system structured as shown in FIG. 5 in Example 1 is
used for a 0.6 mm thickness substrate. With respect to the
substrate, the thickness of which is larger than 0.6 mm, a lens 601
of long focal length held in the lens frame which is integrally
formed with a diaphragm 602, is used. With respect to the
substrate, the thickness of which is smaller than 0.6 mm, a lens
603 of a short focal length held in the lens frame which is
integrally formed with a lens 602, is used. A single lens is held
by a single frame, and these lenses can be switched by driving the
frame with a motor or a solenoid. Further, when a diaphragm is also
provided in the lens frame, the spot size can be easily
switched.
EXAMPLE 7
In this example, the same optical system as that in Example 2 is
used, and the thickness of the system units is reduced. In FIG. 15,
the lens 3 is held by the lens frame 801, the rotation center of
which is caused to coincide with a crossing point of the optical
axis of the deflection mirror 15. In the case of a 0.6 mm thickness
substrate, the lens 3 is located on the side of the objective lens
6 (shown by a dotted line), and in the case of a 1.2 mm thickness
substrate, this frame is rotated by 90.degree., and the lens 3 is
located on the side of the laser beam source (shown by a solid
line). The diaphragm 802 is also integrally provided in the lens
frame, and when this lens frame 801 is rotated, movement of the
lens position and switching of the diaphragm can be simultaneously
carried out, resulting in lowered cost.
In Examples, the divergent degree is changed before and after the
start of the reproduction of the optical information recording
medium, and at the time of correction for temperature and humidity
variation. When the divergent degree is not changed, the output of
the motor, constituting the moving means to move the divergence
changing means, can be used for other purposes, such as a driving
source of the optical pick-up apparatus, in the direction of the
inner and outer periphery; and a driving source for tilt-adjustment
by which warpage of the substrate is detected and at least the
objective lens actuator portion of the information pick-up
apparatus is tilted.
Although the cases corresponding to two types of substrates having
0.6 mm thickness and 1.2 mm thickness are mainly shown in the above
Examples, it is of course obvious that the present invention can
correspond to various kinds of thickness other than the two kinds
of thickness above-described. Further, an optical information
recording medium having two informaiton recording surfaces
corresponding to the front and rear surfaces of one transparent
substrate can be reproduced from the same direction.
Further, the present invention is not limited to the exclusive
reproducing method, but any recording method can be utilized.
In the optical disk apparatus using the optical pick-up apparatus
described in Examples, when the optical information recording
medium, (which is called an optical disk hereinafter), is read, a
judging means for judging the thickness of the substrate of the
optical disk which is loaded in the optical disk apparatus, is
provided, and the divergent degree of the luminous flux entering
into the objective lens is set corresponding to the information by
the judging means. This judging means may be structured by at least
a thickness detecting means, and a common logic circuit such as
CPU, or the like.
The thickness detection means is realized by the following
methods.
A. Thickness information is detected through a switch from an
optical disk cartridge having the thickness information.
B. In the case of the optical disk, the outer diameter of which is
different corresponding to the thickness, the difference of the
outer diameter is detected by a photointerrupter, or the like.
C. A switch for setting information corresponding to the substrate
thickness is provided outside of the optical disk apparatus, and
the thickness information is detected by the status of the
switch.
D. A thickness detection optical system composed of LEDs,
phototransistors, or the like, is provided opposite to the loaded
optical disk, and the thickness information is discriminated based
on the output of this optical system.
E. The objective lens of the optical pick-up apparatus is driven in
the upper and lower directions by using an actuator for a focusing
drive, and the movement amount of the objective lens moved while
the reflected light from the front and rear surfaces of the
substrate is detected based on the movement time.
F. The luminous flux incident surface-side of the optical disk is
held as the reference by a spindle motor, the objective lens of the
optical pick-up apparatus is vertically driven by using an actuator
for focusing drive, and the position at which the focused point is
generated by a focus error signal from the information recording
surface, is detected according to the driving current value or
driving time.
G. When the luminous flux entering into the objective lens is on
the fist divergent degree corresponding to 0.6 mm thickness
substrate, the objective lens is vertically driven with respect to
the rotating optical disk by using an actuator for focusing drive,
and the focus error signal is detected. The substrate thickness is
detected by discriminating whether a predetermined information
signal or track error signal is detected or not in the vicinity of
the focused point.
Even if the optical disk apparatus can read the optical disks
having a plurality of types of the substrate thickness, when the
optical disk having the similar thickness and shape can be loaded
into the apparatus, it is required to discriminate whether the
optical disk is presumed type disk or not, simultaneously with
discrimination of the thickness. For this purpose, it may be
detected whether the signal from the information recording surface
of the optical disk is a presumed type disk or not.
For this purpose, when the luminous flux entering into the
objective lens is at the second divergent degree corresponding to,
for example, the 1.2 mm thickness substrate, the optical disk is
rotated at a predetermined first rotation speed (for example, 1500
rpm) by a spindle motor, and the objective lens is vertically
driven by an actuator for focusing drive. When the information
signal having a predetermined frequency component is not detected
in the vicinity of the focused point of the focusing error signal,
or when a predetermined information signal is not detected after
the focusing servo operation or the tracking servo operation has
been carried out, then, the control means, composed of a CPU or the
like, moves the divergence changing means using the moving means so
that the divergent degree is changed to the second one
corresponding to, for example, the 0.6 mm thickness substrate.
When the information pick-up apparatus in Example 1 is used, the
lens which is the divergence changing means is moved by the moving
means and the divergent degree of the luminous flux entering into
the objective lens can be changed under the condition that the
focusing and tracking servo operations are carried out. In the case
of the information pick-up apparatus in Examples 2 and 3, time of
laser beam interruption is increased, and the servo operation tends
to be unstable. Accordingly, the divergent angle may be changed
after the servo operation is stopped once.
After the divergent angle has been changed, the information signal
is detected again. When the predetermined information is not
obtained, the optical disk is ejected from the apparatus because it
is not a presumed type disk.
Further, in the optical disk apparatus which can read the optical
disks having a plurality of types of substrate thickness, the
optical disk is rotated at a predetermined second rotation speed
(for example, 1500 rpm) under the condition that the divergent
degree is set at the second one corresponding to, for example, a
1.2 mm thickness substrate, in order to read the optical disks
having the same thickness but a different reference rotation
number. When the signal, including a predetermined frequency
component, can not be detected under the condition that at least
the focusing servo operation is carried out, or when the signal can
be detected as the signal from the optical disk of the type to be
rotated at the first rotation speed (for example, 500 rpm), the
rotation speed is changed to the first rotation speed.
In the case where the divergent degree or the rotation speed is
changed, when the pitch of the information track of the optical
disk from which reading is presumed after the change, is different
from the original setting, it is preferable that the diaphragm
means for changing the diameter of the luminous flux is
simultaneously controlled so that NA is changed to obtain a
desirable spot size.
Further, when a tracking error in the 3-beam method is detected,
the angle of the 0-order light and .+-.1-order light with respect
to the information track is simultaneously changed.
The refractive index of optical members made of glass, plastic, or
the like, and the wavelength of a laser beam source vary due to
temperature and humidity. Further, members holding those optical
members also expand and contract, and thereby, the intervals
between optical members vary. Accordingly, spherical aberration is
generated due to variations of temperature and humidity. This
aberration can be corrected when the position of the divergence
degree moving means is controlled.
In order to correct variations of temperature and humidity, after
at least the focusing servo operation is carried out on the
information recording surface 8 of the optical informaiton
recording medium, the position of the divergence degree changing
means is moved so that the amplitude of the reproduced signal
becomes larger, or jittering is reduced. Further, when the
above-described motions are carried out during information
reproduction, or during waiting under the condition that at least
the focusing servo operation is carried out, the optimum
information recording and reproducing can be carried out.
As described above, according to the present invention, optical
information recording mediums having different substrate thickness
can be recorded and reproduced by a single information pick-up
apparatus, and an information pick-up apparatus and an information
recording medium apparatus which have interchageability with a
plurality of substrate thickness, and which have a simple structure
and are low in cost, can be realized.
Further, only one optical spot is used for recording and writing,
and thereby, power loss is minimized. Accordingly, the S/N ratio is
increased in reading, and writing can be carried out by lower laser
power in recording.
Still further, only one objective lens is used in the system, and
thereby, the size and weight of movable portions of an actuator to
drive the objective lens, can be reduced, and consumed current is
reduced. Further, the sensitivity can easily be increased, and this
apparatus can easily correspond to high speed rotation of the
information recording medium.
Further, this apparatus can easily correspond to arbitrary
substrate thickness, and fluctuations of the substrate thickness
can be easily corrected.
Next, Examples (8 to 11) according to the first and second
embodiments to attain the first object of the present invention
will be described. In the example of numerical values in each
example, the distance between the i-th surface and the (i+1)th
surface on the optical axis at the position (the first position)
for the 0.6 mm substrate thickness is represented by d1i, and that
at the position (the second position) for the 1.2 mm substrate
thickness is represented by d2i.
EXAMPLE 8
______________________________________ Thickness of the transparent
substrate 0.6 mm (t1) 1.2 mm (t2) Distance between surfaces d1i d2i
Diaphragm diameter .phi.4.08 .phi.4.08 Magnification ratio of the
entire optical system -1/7.9 -1/6.2 NA on the information recording
surface-side 0.60 0.59 Focal length of the divergence changing lens
f.sub.c = 26.85 (mm) Focal length of the objective lens f.sub.o =
3.40 (mm) Focal length of the entire optical system at a
transparent substrate thickness of t.sub.1 f.sub.T = 3.53 (mm)
______________________________________ i ri d1i d2i ni
______________________________________ 0 0.55 0.55 1.0 1 .infin.
3.00 3.00 1.51455 2 .infin. 22.05 12.40 1.0 3 39.8985 2.00 2.00
1.80186 4 13.6343 3.00 3.00 1.58701 5 -17.4703 3.00 12.83 1.0 6
Diaphragm (.infin.) 0.00 0.00 1.0 7 2.0500 2.60 2.60 1.49005 8
-5.1870 1.60 1.42 1.0 9 .infin. 0.60 1.20 1.58 10 Information
recording surface (.infin.) ______________________________________
Aspherical data of i = 7 surface .kappa. = -0.46211 A.sub.1 =
-0.81009 .times. 10.sup.-3 P.sub.1 = 4.0000 A.sub.2 = -0.18077
.times. 10.sup.-3 P.sub.2 = 6.0000 A.sub.3 = -0.23378 .times.
10.sup.-4 P.sub.3 = 8.0000 A.sub.4 = -0.87100 .times. 10.sup.-5
P.sub.4 = 10.0000 ______________________________________ Aspherical
data of i = 8 surface .kappa. = -20.447 A.sub.1 = 0.91069 .times.
10.sup.-2 P.sub.1 = 4.0000 A.sub.2 = -0.35507 .times. 10.sup.-2
P.sub.2 = 6.0000 A.sub.3 = 0.78952 .times. 10.sup.-3 P.sub.3 =
8.0000 A.sub.4 = -0.68843 .times. 10.sup.-4 P.sub.4 = 10.0000
______________________________________
FIG. 18 is a graph showing the relationship between a movement
amount of the divergence changing lens in Example 8 and the
spherical aberration.
FIGS. 19(a), 19(b), 21(a), 21(b), 23(a), 23(b), 25(a) and 25(b) are
views showing optical paths respectively for a 0.6 mm transparent
substrate thickness and a 1.2 mm transparent substrate thickness in
Example 8 and Examples 9, 10 and 11, which will be described
later.
In the optical systems shown in Examples 8, 9, 10 and 11, FIGS.
20(a), 22(a), 24(a) and 26(a) are views respectively showing the
spherical aberration for a 0.6 mm transparent substrate thickness.
FIGS. 20(b), 22(b), 24(b) and 26(b) are views respectively showing
the sherical aberration when the 1.2 mm thickness transparent
substrate is inserted while respective divergence changing lenses
are arranged for a 0.6 mm transparent substrate thickness. FIGS.
20(c), 22(c), 24(c) and 26(c) are views respectively showing the
spherical aberration when 0.6 mm thickness transparent substrate is
inserted while respective divergence changing lenses are arranged
for a 1.2 mm thickness transparent substrate. FIG. 20(d), 22(d),
24(d) and 26(d) are views respectivly showing the spherical
aberration when the lens is adjusted for a 1.2 mm transparent
substrate thickness.
EXAMPLE 9
______________________________________ Thickness of the transparent
substrate 0.6 mm (t1) 1.2 mm (t2) Distance between surfaces d1i d2i
Diaphragm diameter .phi.4.08 .phi.4.08 Magnification ratio of the
entire optical system -1/8.0 -1/6.2 NA on the information recording
surface-side 0.60 0.59 Focal length of the divergence changing lens
f.sub.C = 26.85 (mm) Focal length of the objective lens f.sub.O =
3.40 (mm) Focal length of the entire optical system at a
transparent substrate thickness of t.sub.1 f.sub.T = 3.41 (mm)
______________________________________ i ri d1i d2i ni
______________________________________ 0 Source 0.55 0.55 1.0 1
.infin. 3.00 3.00 1.51455 2 .infin. 23.90 14.15 1.0 3 -156.0000
1.20 1.20 1.82920 4 -19.5513 3.00 12.93 1.0 5 Diaphragm (.infin.)
0.00 0.00 1.0 6 2.0500 2.60 2.60 1.49005 7 -5.1870 1.60 1.42 1.0 8
.infin. 0.60 1.20 1.58 9 Information recording surface (.infin.)
______________________________________ Aspherical data of i = 6
surface .kappa. = -0.46211 A.sub.1 = -0.8100910.sup.-3 P.sub.1 = 4
A.sub.2 = -0.18077 .times. .times. 10.sup.-3 P.sub.2 = 6 A.sub.3 =
-0.23378 .times. 10.sup.-4 P.sub.3 = 8 A.sub.4 = -0.87100 .times.
10.sup.-5 P.sub.4 = 10 ______________________________________
Aspherical data of i = 7 surface .kappa. = -20.447 A.sub.1 =
0.91069 .times. 10.sup.-2 P.sub.1 = 4 A.sub.2 = -0.35507 .times.
10.sup.-2 P.sub.2 = 6 A.sub.3 = 0.78952 .times. 10.sup.-3 P.sub.3 =
8 A.sub.4 = -0.68843 .times. 10.sup.-4 P.sub.4 = 10
______________________________________
EXAMPLE 10
______________________________________ Thickness of the transparent
substrate 0.6 mm (t1) 1.2 mm (t2) Distance between surfaces d1i d2i
Diaphragm diameter .phi.4.08 .phi.4.08 Magnification ratio of the
entire optical system -1/8.0 -1/6.1 NA on the information recording
surface-side 0.60 0.59 Focal length of the divergence changing lens
f.sub.C = 26.85 (mm) Focal length of the objective lens f.sub.O =
3.40 (mm) Focal length of the entire optical system at a
transparent substrate thickness of t.sub.1 f.sub.T = 3.34 (mm)
______________________________________ i ri d1i d2i ni
______________________________________ 0 Source 0.55 0.55 1.0 1
.infin. 3.00 3.00 1.51455 2 .infin. 23.90 14.51 1.0 3 -156.0000
1.20 1.20 1.82920 4 -19.5513 3.00 12.58 1.0 5 Diaphragm (.infin.)
0.00 0.00 1.0 6 2.4000 2.60 2.60 1.69404 7 -78.2277 1.51 1.32 1.0 8
.infin. 0.60 1.20 1.58 9 Information recording surface (.infin.)
______________________________________ Aspherical data of i = 6
surface .kappa. = -0.22769 A.sub.1 = -0.14079 .times. 10.sup.-2
P.sub.1 = 4 A.sub.2 = -0.18562 .times. 10.sup.-3 P.sub.2 = 6
A.sub.3 = -0.22586 .times. 10.sup.-4 P.sub.3 = 8 A.sub.4 = -0.24870
.times. 10.sup.-5 P.sub.4 = 10 Aspherical data of i = 7 surface
.kappa. = -21.22 A.sub.1 = 0.11864 .times. 10.sup.-1 P.sub.1 = 4
A.sub.2 = -0.32315 .times. 10.sup.-2 P.sub.2 = 6 A.sub.3 = 0.89784
.times. 10.sup.-3 P.sub.3 = 8 A.sub.4 = -0.65119 .times. 10.sup.-4
P.sub.4 = 10 ______________________________________
EXAMPLE 11
______________________________________ Thickness of the transparent
substrate 0.6 mm (t1) 1.2 mm (t2) Distance between surfaces d1i d2i
Diaphragm diameter .phi.4.08 .phi.4.08 Magnification ratio of the
entire optical system -1/11.8 -1/8.9 NA on the information
recording surface-side 0.60 0.59 Focal length of the divergence
changing lens f.sub.C = 26.85 (mm) Focal length of the objective
lens f.sub.O = 3.40 (mm) Focal length of the entire optical system
at a transparent substrate thickness of t.sub.1 f.sub.T = 3.31 (mm)
______________________________________ i ri d1i d2i ni
______________________________________ 0 Source 0.55 0.55 1.0 1
.infin. 3.00 3.00 1.51455 2 .infin. 36.96 16.22 1.0 3 -339.3412
1.20 1.20 1.82920 4 -30.2635 3.00 23.92 1.0 5 Diaphragm (.infin.)
0.00 0.00 1.0 6 2.0500 2.60 2.60 1.49005 7 -5.1870 1.60 1.42 1.0 8
.infin. 0.60 1.20 1.58 9 Information recording surface (.infin.)
______________________________________ Aspherical data of i = 6
surface .kappa. = -0.46211 A.sub.1 = -0.81009 .times. 10.sup.-3
P.sub.1 = 4 A.sub.2 = -0.18077 .times. 10.sup.-3 P.sub.2 = 6
A.sub.3 = -0.23378 .times. 10.sup.-4 P.sub.3 = 8 A.sub.4 = -0.87100
.times. 10.sup.-5 P.sub.4 = 10 Aspherical data of i = 7 surface
.kappa. = -20.447 A.sub.1 = 0.91069 .times. 10.sup.-2 P.sub.1 = 4
A.sub.2 = -0.35507 .times. 10.sup.-2 P.sub.2 = 6 A.sub.3 = 0.78952
.times. 10.sup.-3 P.sub.3 = 8 A.sub.4 = -0.68843 .times. 10.sup.-4
P.sub.4 = 10 ______________________________________
2. Examples (12-24) relating to the third and fourth embodiments to
attain the first object will be described below.
Each example (12-24) includes the following numerical values. A
laser beam source is defined as the zero-th surface, and the radius
of curvature of the i-th surface, (including a diaphragm surface),
counted from the zero-th surface in order, is expressed by ri, an
interval between the i-th surface and the (i+1) -th surface is
expressed by di, and a refractive index of a medium between the
i-th surface and the i+1-th surface in the wavelength of a luminous
flux of the laser beam source is expressed by ni. The refractive
index of air is defined as 1.
In the case where an aspherical surface is used for a lens surface,
the shape of the aspherical surface is expressed by the following
equation when the conical coefficient is k, the aspherical surface
coefficient is Ai, and the numerical exponent of the aspherical
surface is Pi in an orthogonal coordinate system in which the
vertex of the surface is the origin, and the direction of the
optical axis is defined as the X-axis. ##EQU3##
Initially, Examples 12 and 13 will be described below.
EXAMPLE 12
As Example 12, the structure of FIGS. 27 and 28 will be
described.
A projecting and receiving unit 302, in which a semiconductor laser
chip 1, hologram beam splitter 2, and light detector 9 are
integrally provided, is held by a moving means 301 by which the
projecting and receiving unit 302 is moved in the direction of the
optical axis along which the laser beam advances to the objective
lens 6. The divergent degree of the luminous flux entering into the
objective lens 6 can be changed when the projecting and receiving
unit 302 is moved in the optical axis direction.
The optical system structured as shown in FIG. 27 is arranged at a
position in which the laser beam source, corresponding to
information reading from the optical information recording medium
of the first substrate of 0.6 mm thickness, is located at the first
position.
The specifications of the optical system structured as shown in
FIG. 27 are as follows.
______________________________________ i ri di ni
______________________________________ 0 0.55 1 1 .infin. 3.0
1.514546 2 .infin. 21.62 1 3 90.325 1.5 1.4981 4 -14.364 2.7 1 5
Diaphragm .infin. 0 1 (.phi.3.998) 6 2.0282 2.6 1.4981 7 -5.2236
1.531 1 8 .infin. 0.6 1.58 9 Information recording surface
______________________________________ Aspherical surface
coefficient of i = 3 .kappa. = -290.104 A.sub.1 = -1.5229 .times.
10.sup.-5 P.sub.1 = 4.0000 A.sub.2 = 2.9716 .times. 10.sup.-5
P.sub.2 = 6.0000 A.sub.3 = -4.9564 .times. 10.sup.-6 P.sub.3 =
8.0000 A.sub.4 = 2.9132 .times. 10.sup.-7 P.sub.4 = 10.0000
Aspherical surface coefficient of i = 4 .kappa. = 0.20030 A.sub.1 =
-1.4252 .times. 10.sup.-5 P.sub.1 = 4.0000 A.sub.2 = 2.5238 .times.
10.sup.-5 P.sub.2 = 6.0000 A.sub.3 = -3.8308 .times. 10.sup.-6
P.sub.3 = 8.0000 A.sub.4 = 2.1154 .times. 10.sup.-7 P.sub.4 =
10.0000 ______________________________________
In this connection, aspherical surface coefficients i=6 and i=7 are
the same as those in Example 1.
NA on the information recording surface-side 0.60
NA on the laser beam source-side 0.080
Magnification ratio between the information recording surface and
the laser beam source 0.1331
Wavefront aberration on the axis 0.002 .lambda.rms
Wavefront aberration of the objective lens in the case of 0.1 mm
shift 0.002 .lambda.rms
In this structure, the same lens as that in Examples 1 is used as
the objective lens 6, and a lens, in which the aspherical surface
is used and the spherical surface is accurately corrected, is used
as the lens 3 which is a divergence changing means. Then, almost
non-aberration parallel luminous flux is entered into the objective
lens 6 so that the aberration does not vary even when the objective
lens 6 is shifted at the time of tracking.
In FIG. 28, the light projecting and receiving unit 302 is moved
toward the second position of the objective lens 6 side in order to
correspond to the 1.2 mm substrate thickness. In the structure of
the optical system at this time, intervals between respective
surfaces change as follows with respect to FIG. 27.
______________________________________ d2 from 21.62 to 14.0 d4 2.7
to 1.1 d5 0 to 2.0 d7 1.531 to 1.343
______________________________________
An i=5 is the diaphragm surface, and in FIG. 27, it is a diaphragm
integrally movable with the objective lens 6, and further in FIG.
28, it is an iris diaphragm 303 inserted between the lens 3 and the
objective lens 6.
NA on the information recording surface-side 0.55 (a diaphragm
diameter .phi.3.724)
NA on the laser beam source-side 0.104
Magnification ratio between the information recording surface and
the laser beam source -0.190
Wavefront aberration on the axis 0.005 .lambda.rms
Wavefront aberration of the objective lens in the case of 0.1 mm
shift 0.022 .lambda.rms
In this example, a hologram is used as the beam splitter, and the
semiconductor laser and the light detector are used in proximity to
each other. The size of this optical system can easily be reduced,
and it is easily moved. It is preferable that a half mirror, a
polarization beam splitter, or the like, is used as the beam
splitter, and even when the laser beam source and the light
detector are structured separate from each other, these are
integrated and can be moved in the direction of the optical axis of
the objective lens.
When the diaphragm diameter of the iris diaphragm 303 is reduced
and NA on the side of the information recording surface is
approximately 0.42, NA on the side of the laser beam source is
approximately 0.08. Even when the substrate thickness is changed,
NA on the side of the laser beam source is almost the same, and the
light emergence efficiency or an amount of the light returning to
the light detector is also almost the same. Accordingly, a laser
light-amount control system and a signal detection system is easily
structured.
EXAMPLE 13
In this example, the same optical system as that in Example 12 is
used, and thinner information pick-up is used. In FIG. 29, a
deflection mirror 15 is arranged between the objective lens 6 and
the lens 3, so that the optical path is deflected by 90.degree.. A
top of the light projecting and receiving unit 302 is integrally
provided with a diaphragm 701 which is arranged between the
objective lens 6 and the deflection mirror 15 when the unit is
moved to the position corresponding to a 1.2 mm thickness
substrate, and the diaphragm is simultaneously switched by only
movement of the projecting and receiving unit, resulting in low
cost.
In the case of tracking by the 3-beam method, when a diffraction
grating is arranged between the semiconductor laser and the beam
splitter 2, and the light projecting and receiving unit 302,
composed of a semiconductor laser 1, receiving means 9, beam
splitter 2 and diffraction grating, is structured as a feeding
guide, by which this unit 302 is slightly rotated (by about
1.degree.) around the optical axis when the unit 302 is moved
corresponding to the thickness of the substrate, the azimuth of the
3-beams can be most appropriately adjusted simultaneously
corresponding to the track pitch of the information recording
surface.
Next, Examples (14 to 17) according to the third and fourth
embodiments to attain the first object of the present invention,
will be described. Conditions of numerical values in each example,
are the same as those in the above Examples (8 to 13).
In these examples (14-17), the wavelength of the light beam source
1=635 nm, and in the thickness of transparent substrate, the first
thickness corresponding to the first position t1 =0.6 mm, and the
second thickness corresponding to the second position t2 =1.2 mm.
In this case, the refractive index n=1.58 at the wavelength of the
light beam source.
Further, the numerical aperture NA1 on the information recording
surface-side at the first position is set to 0.6.
In the numerical aperture NA2 on the information recording
surface-side at the second position, simulation for review is
carried out with respect to the aberration view and a change of the
wavefront aberration by presuming the case where the same diaphragm
(the same diaphragm diameter .phi.A1 at the same position with
respect to the objective lens) as that at the first position, is
used. In this case, however, it may also be allowed that the
diaphragm diameter is adjustable and is smaller than .phi.A1. When
the diaphragm diameter is made smaller than .phi.A1, it is clear
that the NA2 value is reduced, and the amount of the aberration and
the amount of the wavefront aberration are decreased less than
those at .phi.A1.
In the following table, f.sub.0 is the focal length of the
objective lens, U1 and U2 are the distances between the light beam
source and the information recording surface of the information
recording medium respectively at the first position and the second
position (the distance between an object and the image), and m1 and
m2 respectively represent the lateral magnification of the
objective lens at the first position and the second position.
T1 and T2 respectively represent the distance from the objective
lens, at the first position and the second position, to the light
beam source (the direction forward from the light beam source
toward the information recording medium is positive).
EXAMPLE 14
______________________________________ f.sub.0 = 3.2410959 1st
position T1 = -34.713 U1 = 40.000 m1 = -0.1000 2nd position T2 =
-22.383 U2 = 28.089 m2 = -0.1614
______________________________________ ri d1i d2i ni
______________________________________ 1 2.080 3.10 3.10 1.49446 2
-3.539 1.587 1.406 3 .infin. 0.60 1.2 1.58000 4 .infin.
______________________________________ Aspherical coefficient 1st
surface .kappa. = -6.08630 .times. 10.sup.-1 A.sub.1 = -4.27090
.times. 10.sup.-4 P.sub.1 = 4.0000 A.sub.2 = -1.49720 .times.
10.sup.-4 P.sub.2 = 6.0000 A.sub.3 = -1.04560 .times. 10.sup.-6
P.sub.3 = 8.0000 A.sub.4 = -4.67950 .times. 10.sup.-7 P.sub.4 =
10.0000 2nd surface .kappa. = -1.36490 .times. 10 A.sub.1 = 3.72820
.times. 10.sup.-3 P.sub.1 = 4.0000 A.sub.2 = -2.85100 .times.
10.sup.-4 P.sub.2 = 6.0000 A.sub.3 = 1.49930 .times. 10.sup.-5
P.sub.3 = 8.0000 A.sub.4 = 1.89980 .times. 10.sup.-9 P.sub.4 =
10.0000 ______________________________________
The distance di from the light beam source to the objective lens
with respect to each transparent substrate is expressed as
follows.
Accordingly, the amount of movement of the light beam source is
expressed as follows.
Since .DELTA.t=t2-t1=0.6 mm,
When the same diaphragm (the diaphragm having the same diaphragm
diameter at the same position with respect to the objective lens)
is used with respect to the first position and the objective lens,
the numerical aperture at the second position NA2max is expressed
as follows.
When NA2=NA2.sub.max =0.595,
When the diaphragm diameter is adjustable and the numerical
aperture at the second position NA2=0.53,
When the numerical aperture at the second position NA2=0.45
When NA2=0.38
The first position and the second position in Example 14 are shown
in FIGS. 30(a) and 30(b). Views of the aberration when NA2=NA2max
are shown in FIGS. 31(a), 31(b) and 31(c). FIG. 31(a) is the view
of the aberration at the first position when t1=0.6 mm. FIG. 31(b)
is the view of the aberration at the first position when the
thickness of the transparent substrate t2=1.2 mm. At this time, the
spherical aberration moves toward the "overcorrected" range. The
view of the spherical aberration at the second position when t2=1.2
mm is shown in FIG. 31(c). In this case, the spherical aberration
is almost corrected.
FIG. 32 shows a change of the wavefront aberration value when the
light beam source is moved so that the spherical aberration becomes
minimum at each thickness of the transparent substrates in the case
where the thickness of the transparent substrate is changed from
0.6 mm to 1.2 mm in Example 14. In this case, the numerical
aperture NA1=0.60 at a 0.6 mm transparent substrate thickness, and
the numerical aperture NA2 at a 1.2 mm transparent substrate
thickness is as follows, NA2=NA2.sub.max =0.595. In these cases,
the numerical apertures are respectively in the vicinity of
NA0.6.
Although the wavefront aberration value is 0.015 .lambda.rms when
t=1.2 mm, this value is sufficiently smaller than Marechal
criterion, consequently is at the level in which no problems
occur.
EXAMPLE 15
______________________________________ f.sub.0 = 3.3763632 1st
position T1 = -29.470 U1 = 35.000 m1 = -0.1250 2nd position T2 =
-20.819 U2 = 26.768 m2 = -0.1839
______________________________________ ri d1i d2i ni
______________________________________ 1 2.180 3.10 3.10 1.49446 2
-3.775 1.830 1.649 3 .infin. 0.60 1.2 1.58000 4 .infin.
______________________________________ Aspherical coefficient 1st
surface .kappa. = -5.56960 .times. 10.sup.-1 A.sub.1 = -1.38700
.times. 10.sup.-3 P.sub.1 = 4.0000 A.sub.2 = -2.05900 .times.
10.sup.-4 P.sub.2 = 6.0000 A.sub.3 = -5.04330 .times. 10.sup.-6
P.sub.3 = 8.0000 A.sub.4 = -7.19700 .times. 10.sup.-7 P.sub.4 =
10.0000 2nd surface .kappa. = -1.27410 .times. 10 A.sub.1 = 2.53780
.times. 10.sup.-3 P.sub.1 = 4.0000 A.sub.2 = -1.10930 .times.
10.sup.-4 P.sub.2 = 6.0000 A.sub.3 = 1.24000 .times. 10.sup.-5
P.sub.3 = 8.0000 A.sub.4 = -2.74030 .times. 10.sup.-7 P.sub.4 =
10.0000 ______________________________________ .increment.d = T1 -
T2 = -8.651 G = -1.1446 NA1 = 0.6 NA2.sub.max = 0.596 When NA2 =
NA2.sub.max = 0.596 NA1 .multidot. .vertline.m1.vertline. = 0.0750
NA2 .multidot. .vertline.m2.vertline. = 0.1097 and
.vertline.m1.vertline. .multidot. f.sub.0 .multidot. NA1.sup.4 =
0.0547 .vertline.m2.vertline. .multidot. f.sub.0 .multidot.
NA2.sup.4 = 0.0784 When the numerical aperture NA2 = 0.53, NA2
.multidot. .vertline.m2.vertline. = 0.0975 .vertline.m2.vertline.
.multidot. f.sub.0 .multidot. NA2.sup.4 = 0.0490 When the numerical
aperture NA2 = 0.45, NA2 .multidot. .vertline.m2.vertline. = 0.0828
.vertline.m2.vertline. .multidot. f.sub.0 .multidot. NA2.sup.4 =
0.0255 When NA2 = 0.38, NA2 .multidot. .vertline.m2.vertline. =
0.0699 .vertline.m2.vertline. .multidot. f.sub.0 .multidot.
NA2.sup.4 ______________________________________ = 0.0129
In the same manner as in Example 14, the first arc second
arrangements in Examples 15, 16 and 17 are respectively shown in
FIGS. 33(a), 33(b), 36(a), 36(b), 39(a) and 39(b). Views of
spherical aberation at NA2=NA2.sub.max are respectively shown in
FIGS. 34(a) to 34(c), 37(a) to 37(c), and 40(a) to 40(c). FIGS.
34(a), 37(a) and 40(a) are views of spherical aberration
respectively at the first arrangement at t1=0.6 mm. FIGS. 34(b),
37(b) and 40(b) are views of spherical aberration respectively at
the first arrangement of the transparent substrate at the thickness
t2=1.2 mm. In this case, the spherical aberration moves to the
"overcorrected"-range. Views of the sperical aberration at the
second arrangement at t2=1.2 mm are respectively shown in FIGS.
34(c), 37(c) and 40(c). In this case, the spherical aberration is
almost corrected. FIGS. 35, 38 and 41 show changes of the wave
front aberration when the light beam source is moved so that the
spherical aberration becomes minimum at respective thicknesses of
the transparent substrates in cases where the thickness of the
transparent substrate is changed from 0.6 mm to 1.2 mm, in Examples
15, 16 and 17.
EXAMPLE 16
______________________________________ f.sub.0 = 3.0107542 1st
position T1 = -45.217 U1 = 50.00 m1 = -0.07000 2nd position T2 =
-24.567 U2 = 29.764 m2 = -0.13465 ri d1i d2i ni
______________________________________ 1 1.911 2.800 2.800 1.49446
2 -3.469 1.383 1.197 3 .infin. 0.600 1.200 1.58000 4 .infin.
______________________________________ Aspherical coefficient
______________________________________ 1st surface k = -6.04930
.times. 10.sup.-1 A.sub.1 = 1.24640 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = -1.49370 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.36210 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-2.95790 .times. 10.sup.-7 P.sub.4 = 10.0000 2nd surface k =
-1.57360 .times. 10 A.sub.1 = 5.52940 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -5.47660 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 2.58450 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
1.12380 .times. 10.sup.-6 P.sub.4 = 10.0000 .increment.d = T1 - T2
= -20.650 G = -1.1696 NA1 = 0.6 NA2.sub.max = 0.596 When NA2 =
NA2.sub.max = 9.596, NA1 .multidot. .vertline.m1.vertline. = 0.0420
and NA2 .multidot. .vertline.m2.vertline. = 0.0805
.vertline.m1.vertline. .multidot. f.sub.0 .multidot. NA1.sup.4 =
0.0273 .vertline.m2.vertline. .multidot. f.sub.0 .multidot.
NA2.sup.4 = 0.0513 When NA2 = 0.53, NA2 .multidot.
.vertline.m2.vertline. = 0.0718 .vertline.m2.vertline. .multidot.
f.sub.0 .multidot. NA2.sup.4 = 0.0321 When NA2 = 0.45, NA2
.multidot. .vertline.m2.vertline. = 0.0608 .vertline.m2.vertline.
.multidot. f.sub.0 .multidot. NA2.sup.4 = 0.0167 When NA2 = 0.38,
NA2 .multidot. .vertline.m2.vertline. = 0.0513
.vertline.m2.vertline. .multidot. f.sub.0 .multidot. NA2.sup.4 =
______________________________________ 0.0085
EXAMPLE 17
______________________________________ f.sub.0 = 3.1052331 1st
position T1 = -24.956 U1 = 30.000 m1 = -0.14000 2nd position T2 =
-17.998 U2 = 23.460 m2 = -0.20400 ri d1i d2i ni
______________________________________ 1 2.580 2.600 2.600 1.72623
2 -10.323 1.844 1.662 3 .infin. 0.600 1.200 1.58000 4 .infin.
______________________________________ Aspherical coefficient
______________________________________ 1st surface k = -7.75620
.times. 10.sup.-1 A.sub.1 = 9.49130 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = 3.31790 .times. 10.sup.-4 P.sub.2 = 6.0000 A.sub.3
= 4.71180 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 = -3.48490
.times. 10.sup.-6 P.sub.4 = 10.0000 2nd surface k = -1.63440
.times. 10 A.sub.1 = 7.67570 .times. 10.sup.-3 P.sub.1 = 4.0000
A.sub.2 = -1.52800 .times. 10.sup.-3 P.sub.2 = 6.0000 A.sub.3 =
8.96720 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 = -1.76040
.times. 10.sup.-6 P.sub.4 = 10.0000 .increment.d = T1 - T2 = -6.958
mm G = -1.1455 NA1 = 0.6 NA2.sub.max = 0.593 When NA2 = NA2.sub.max
= 0.593, NA1 .multidot. .vertline.m1.vertline. = 0.0840 NA2
.multidot. .vertline.m2.vertline. = 0.1210 Further,
.vertline.m1.vertline. .multidot. f.sub.0 .multidot. NA1.sup.4 =
0.0563 .vertline.m2.vertline. .multidot. f.sub.0 .multidot.
NA1.sup.4 = ______________________________________ 0.0783
When the diaphragm diameter is adjustable and the numerical
aperture at the second position NA2=0.53,
When the diameter of the diaphragm is changeable and the numerical
aperture at the second position NA2=0.45
When NA2=0.38,
In information recording medium apparatus using the optical pick-up
apparatus described above, when the optical information recording
medium is read out, a discrimination means to discriminate the
thickness of the substrate of the loaded information recording
medium is provided in the information recording medium apparatus,
and the divergence degree of the luminous flux entering into the
objective lens is set according to information by the
discrimination means. This discrimination means can be composed of
at least a thickness detection means and a logic circuit such as
well known CPUs or the like.
The thickness detection means is entirely the same as that in
embodiment 2.
Even when the information recording medium apparatus can read the
information recording medium thicknesses of plural types of
substrates, when the information recording medium in which the
thickness or shape is similar to each other, can be loaded into the
apparatus, it is required to discriminate the thickness, and also
to discriminate whether the kind of information recording medium is
the assumed one or not. In order to meet this requirement, it may
be allowed to detect whether the kind of signals from the
information recording surface of the informaiton recording medium
is an assummed one or not.
For this purpose, the following is carried out in the same manner
as in Embodiment 2: the luminous flux entering into the objective
lens is in the condition of the second divergence degree
corresponding to the substrate thickness of, for example, 1.2 mm;
the information recording medium is rotated at the predetermined
second rotation speed (for example, 1500 rpm) by a spindle motor;
the objective lens is vertically driven by an actuator for focusing
drive; and when the information signal having a predetermined
frequency component can not be detected at the vicinity of the
focused point of a focusing error signal, or when a predetermined
information signal can not be detected after only a focusing
servo-operation has been conducted or a tracking servo-operation
has been conducted, the moving means is controlled by the control
means composed of a CPU or the like, and the laser beam source is
moved so that the first divergence degree corresponding to the
substrate of, for example, 0.6 mm thickness is obtained.
When the optical pick-up apparatus in Example 12 is used, the
position of the laser beam source, and the diameter of the
diaphragm can be changed under the condition that focusing
servo-operations and tracking servo-operations are conducted. In
the case of the optical pick-up apparatus in Example 13, a period
of time, during which the laser beam is interrupted, becomes
longer, and servo-operations tend to be unstable. Accordingly, the
laser beam source is preferably moved after the servo-operation is
stopped once.
After the laser beam source has been moved, the information signal
is accessed again. When the predetermined information is not
obtained, the type of the information recording medium is not the
assumed one, so that this information recording medium is
delivered.
In cases where the divergence degree or rotation speed is changed,
when the pitch of the information track of the information
recording medium which is assumed to be read after change, is
different, then the diaphragm means is preferably controlled so
that the diameter of the simultaneously entering luminous flux is
changed, and the numerical aperture is changed so that a desirable
spot size is obtained.
Further, also in cases where a tracking error is detected by a
3-beam method, it is preferable to change angles of the 0-order
light and .+-.1-order light with respect to the information
track.
The refractive index of optical members made of glass, plastic, or
the like, and the wavelength of laser beam sources vary due to
temperature and humidity. Further, members holding those optical
members also expand and contract, and thereby, intervals between
optical members are changed. Accordingly, spherical aberration is
generated due to variations of temperature and humidity. This
aberration can be corrected when the position of the divergence
degree moving means is controlled.
In order to correct variations of temperature and humidity, after
at least the focusing servo operation is carried out on the
information recording surface 8 of the optical information
recording medium, the position of the divergence degree changing
means is moved so that the amplitude of the reproduced signal
becomes larger, or jittering is reduced. Further, when the
above-described operations are carried out during information
reproduction, or during waiting under the condition that at least
the focusing servo-operation is carried out, optimal information
recording and reproducing can be carried out.
As described in the third and fourth Embodiments, when only the
light beam source is moved, the optical information recording
medium, having a different substrate thickness, can be recorded and
reproduced by one information pick-up apparatus, and an information
pick-up apparatus and an optical disk apparatus can be obtained
which are interchangeable for a plurality of substrate thickness,
and are simple and compact in the structure, and are low in
production cost.
Still further, this apparatus can function with arbitrary substrate
thicknesses, and variation of substrate thickness can also be
easily corrected.
In this connection, although the operation distance changes a
little according to changes of the divergent angle of the light
entering into the objective lens, it is not necessary to consider
this change of the operation distance because it is within the
operation range of the focusing actuator.
Next, Examples (18 to 24) according to the third and the fourth
embodiments to attain the first object of the present invention,
will be described.
EXAMPLE 18
The first position
Composite focal length of the entire system
f.sub.0 =3.7183650
Focal length of the objective lens single body
f.sub.0 =3.241
Distance between the light beam source and the first surface of the
coupling lens
T=-9.838
Lateral magnification of the entire system
mt1=-0.140
Lateral magnification of the objective lens single body
mol=-0.1
Total length of the optical system (distance between the light beam
source and the image formation point)
U=34.623
The second position
Composite focal length of the entire system
F2=3.0168480
Distance between the light beam source and the first surface of the
coupling lens
T=-9.838
Lateral magnification of the entire system
mt2=-0.225
Lateral magnification of the objective lens single body
mo2=-0.161
Total length of the optical system (distance between the light beam
source and the image formation point)
______________________________________ U = 22.179 i ri d1i d2i ni
______________________________________ 1 -5.584 2.00 1.51455 2
-5.315 17.50 5.18 3 2.080 3.10 1.49446 4 -3.539 1.585 1.402 5
.infin. 0.060 1.20 1.58000 6 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -6.08630
.times. 10.sup.-1 A.sub.1 = -4.27090 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = -1.49720 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = -1.04560 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-4.67950 .times. 10.sup.-7 P.sub.4 = 10.0000 4th surface k =
-1.36490 .times. 10 A.sub.1 = 3.72820 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -2.85100 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.49930 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
1.89980 .times. 10.sup.-9 P.sub.4 = 10.0000
______________________________________
The first position and the second position in Example 18 are shown
in FIGS. 42(a) and 42(b). The magnification ratio mc of the
coupling lens is mo1/mt1=0.714, and the coupling lens is set so as
to be image-side NA1 0.6. Also in the second position, the distance
T between the light beam source and the coupling lens, and the
magnification ratio mc of the coupling lens is the same as those in
the first position. The amount of movement of the light beam source
and the coupling lens is as follows.
Further,
then,
When the same diaphragm (the diaphragm having the same diaphragm
diameter and the same position with respect to the objective lens)
is used in the first position and the second position, the
numerical aperture at the second position NA is expressed as
follows,
NA2=0.595.
The spherical aberration is shown in FIGS. 43(a), 43(b) and
43(c).
FIG. 43(a) shows the spherical aberration at the first position at
the time of t1=0.6 mm. FIG. 43(b) shows the spherical aberration at
the first position when the thickness of the transparent substrate
t2=1.2 mm, and the spherical aberration greatly moves to the
"overcorrected" range, so that the diameter of the spot cannot be
reduced. FIG. 43(c) is a view of the spherical aberration at the
second position when t2=1.2 mm, and the aberration is almost
corrected, so that the diameter of the spot can be reduced.
FIG. 44 shows a change of the wavefront aberration value when the
light beam source and the coupling lens are integrally moved so
that the spherical aberration becomes minimum at each thickness of
the transparent substrates in the case where the thickness of the
transparent substrate is changed from 0.6 mm to 1.2 mm. In this
case, the numerical aperture NA is 0.60 at 0.6 mm transparent
substrate thickness, and the numerical aperture NA at 1.2 mm
transparent substrate thickness is 0.595. In these cases, the
numerical apertures are each about NA0.6.
The wavefront aberration value is 0.015 .lambda.rms even when t=1.2
mm, and this value is satisfactorily corrected.
EXAMPLE 19
1st position
______________________________________ F1 = 3.9470247 T = -9.752
mt1 = -0.180 mo1 = -0.125 U = 29.782
______________________________________
2nd position
The lateral magnification ratio of the objective lens single
body
______________________________________ F2 = 3.2389684 T = -9.752
mt2 = -0.265 mo2 = -0.184 U = 21.552 i ri d1i d2i ni
______________________________________ 1 -9.373 2.00 1.51455 2
-7.212 12.50 3.850 3 2.180 3.10 1.49446 4 -3.775 1.830 1.650 5
.infin. 0.60 1.20 1.58000 6 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -5.56960
.times. 10.sup.-1 A.sub.1 = -1.38700 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = -2.05900 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = -5.04330 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-7.19700 .times. 10.sup.-7 P.sub.4 = 10.0000 4th surface k =
-1.27410 .times. 10 A.sub.1 = 2.53780 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -1.10930 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.24000 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
-2.74030 .times. 10.sup.-7 P.sub.4 = 10.0000
______________________________________
The arrangement in Example 19 is shown in FIGS. 45(a) and 45(b),
the spherical aberration is shown in FIGS. 46(a), 46(b) and 46(c),
and a change of the wavefront aberration RMS value according to the
movement is shown in FIG. 47. The aberration in FIGS. 46(a) 46(b)
and 46(c) are the same as that in 43(a), 43(b) and 43(c).
______________________________________ mc = 0.694 .increment.d = d2
- d1 = -8.65 mm G = -1.14479 NA1 = 0.6 NA2 = 0.596
______________________________________
EXAMPLE 20
1st position
______________________________________ F1 = 5.7480506 T = -11.388
mt1 = -0.192 mol1 = -0.070 U = 24.435
______________________________________
2nd position
The lateral magnification ratio of the objective lens single
body
______________________________________ F2 = 3.1419938 T = -11.388
mt2 = -0.192 mo2 = -0.134 U = 24.435 i ri d1i d2i ni
______________________________________ 1 -19.481 2.00 1.51455 2
-11.222 26.50 5.85 3 1.911 2.80 1.49446 4 -3.469 1.382 1.197 5
.infin. 0.60 1.20 1.58000 6 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -6.04930
.times. 10.sup.-1 A.sub.1 = 1.24640 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = -1.49370 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.36210 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-2.95790 .times. 10.sup.-7 P.sub.4 = 10.0000 4th surface k =
-1.57360 .times. 10 A.sub.1 = 5.52940 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -5.47660 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 2.58450 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
1.12380 .times. 10.sup.-7 P.sub.4 = 10.0000
______________________________________
The arrangement in Example 20 is shown in FIGS. 48(a) and 48(b),
the spherical aberration is shown in FIGS. 49(a), 49(b) and 49(c),
and a change of the wavefront aberration value according to the
movement is shown in FIG. 50. The aberration in FIGS. 49(a), 49(b)
and 49(c) are the same as that in 43(a), 43(b) and 43(c).
______________________________________ mc = 0.700 .increment.d = d2
- d1 = -20.65 mm G = -1.16964 NA1 = 0.602 NA2 = 0.598
______________________________________
EXAMPLE 21
1st position
______________________________________ F1 = 10.337302 T = -10.365
mt1 = -0.140 mo1 = -0.070 U = 38.145 2nd position F2 = 2.7318163 T=
-10.365 mt2 = -0.263 mo2 = -0.132 U = 18.179 i ri d1i d2i ni
______________________________________ 1 -8.601 1.50 1.51455 2
-5.471 21.50 1.13 3 1.911 2.80 1.49446 4 -3.469 1.380 1.184 5
.infin. 0.60 1.20 1.58000 6 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -6.04930
.times. 10.sup.-1 A.sub.1 = 1.24640 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = -1.49370 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.36210 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-2.95790 .times. 10.sup.-7 P.sub.4 = 10.0000 4th surface k =
-1.57360 .times. 10 A.sub.1 = 5.52940 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -5.47660 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 2.58450 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
1.12380 .times. 10.sup.-7 P.sub.4 = 10.0000
______________________________________
The arrangement in Example 21 is shown in FIGS. 51(a) and 51(b),
the spherical aberration is shown in FIGS. 52(a), 52(b) and 52(c),
and a change of the wavefront aberration value according to the
movement is shown in FIG. 53. The aberration in FIGS. 52(a), 52(b)
and 52(c) are the same as that in 43(a), 43(b) and 43(c).
______________________________________ mc = 0.500 .increment.d = d2
- d1 = -20.37 mm G = -1.20057 NA1 = 0.602 NA2 = 0.598
______________________________________
EXAMPLE 22
1st position
______________________________________ F1 = 3.3024261 T = -11.779
mt1 = -0.150 mo1 = -0.125 U = 31.809
______________________________________
2nd position
______________________________________ F2 = 3.1287785 T= -11.779
mt2 = -0.221 mo2 = -0.184 U = 23.583 i ri d1i d2i ni
______________________________________ 1 -7.696 2.00 1.51455 2
-7.626 12.50 3.855 3 2.180 3.10 1.49446 4 -3.775 1.830 1.649 5
.infin. 0.60 1.20 1.58000 6 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -5.56950
.times. 10.sup.-1 A.sub.1 = -1.38700 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -2.05900 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = -5.04330 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-7.19700 .times. 10.sup.-7 P.sub.4 = 10.0000 4th surface k =
-1.27410 .times. 10 A.sub.1 = 2.53780 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -1.10930 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.24000 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
-2.74030 .times. 10.sup.-7 P.sub.4 = 10.0000
______________________________________
The arrangement in Example 22 is shown in FIGS. 54(a) and 54(b),
the spherical aberration is shown in FIGS. 55(a), 55(b) and 55(c),
and a change of the wavefront aberration value according to the
movement is shown in FIG. 56. The aberration in FIGS. 55(a), 55(b)
and 55(c) are the same as that in 43(a), 43(b) and 43(c).
______________________________________ mc = 0.833 .increment.d = d2
- d1 = -8.645 mm G = -1.14576 NA1 = 0.600 NA2 = 0.596
______________________________________
EXAMPLE 23
1st position
______________________________________ F1 = 7.1515624 T = -8.092
mt1 = -0.200 mo1 = -0.100 U = 30.377
______________________________________
2nd position
______________________________________ F1 = 3.1178293 T = -8.092
mt2 = -0.320 mo2 = -0.160 U = 18.531 i ri d1i d2i ni
______________________________________ 1 -11.232 2.00 1.51455 2
-5.828 15.00 2.74 3 2.080 3.10 1.49446 4 -3.539 1.585 1.399 1
.infin. 0.60 1.20 1.58000 2 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -6.08630
.times. 10.sup.-1 A.sub.1 = -4.27090 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = -1.49720 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = -1.04560 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 =
-4.67950 .times. 10.sup.-7 P.sub.4 = 10.0000 4th surface k =
-1.36490 .times. 10 A.sub.1 = 3.72820 .times. 10.sup.-3 P.sub.1 =
4.0000 A.sub.2 = -2.85100 .times. 10.sup.-4 P.sub.2 = 6.0000
A.sub.3 = 1.49930 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 =
1.89980 .times. 10.sup.-9 P.sub.4 = 10.0000
______________________________________
The arrangement in Example 23 is shown in FIGS. 57(a) and 57(b),
the spherical aberration is shown in FIGS. 58(a), 58(b) and 58(c),
and a change of the wavefront aberration value according to the
movement is shown in FIG. 59. The aberration in FIGS. 58(a), 58(b)
and 58(c) are the same as that in 43(a), 43(b) and 43(c).
______________________________________ mc = 0.500 .increment.d = d2
- d1 = -12.26 mm G = -1.15434 NA1 = 0.600 NA2 = 0.595
______________________________________
EXAMPLE 24
1st position
______________________________________ F1 = 3.9454953 T = -6.924
mt1 = -0.200 mo1 = -0.100 U = 30.377
______________________________________
2nd position
______________________________________ F1 = 3.1427760 T = -6.924
mt2 = -0.291 mo2 = -0.204 U = 19.932 i ri d1i d2i ni
______________________________________ 1 -9.980 2.00 1.51455 2
-6.831 12.50 5.545 3 2.580 2.60 1.72623 4 -10.323 1.844 1.663 1
.infin. 0.60 1.20 1.58000 2 .infin.
______________________________________ Aspherical coefficient
______________________________________ 3rd surface k = -7.75620
.times. 10.sup.-1 A.sub.1 = 9.49130 .times. 10.sup.-4 P.sub.1 =
4.0000 A.sub.2 = 3.31790 .times. 10.sup.-5 P.sub.2 = 6.0000 A.sub.3
= 4.71180 .times. 10.sup.-6 P.sub.3 = 8.0000 A.sub.4 = -3.48490
.times. 10.sup.-6 P.sub.4 = 10.0000 4th surface k = -1.63440
.times. 10 A.sub.1 = 7.67570 .times. 10.sup.-3 P.sub.1 = 4.0000
A.sub.2 = -1.52800 .times. 10.sup.-3 P.sub.2 = 6.0000 A.sub.3 =
8.96720 .times. 10.sup.-5 P.sub.3 = 8.0000 A.sub.4 = 1.76040
.times. 10.sup.-6 P.sub.4 = 10.0000
______________________________________
The arrangement in Example 24 is shown in FIGS. 60(a) and 60(b),
the spherical aberration is shown in FIGS. 61(a), 61(b) and 61(c),
and a change of the wavefront aberration value according to the
movement is shown in FIG. 62. The aberration in FIGS. 61(a), 61(b)
and 61(c) are the same as that in 43(a), 43(b) and 43(c).
______________________________________ mc = 0.700 .increment.d = d2
- d1 = -6.955 mm G = -1.14619 NA1 = 0.600 NA2 = 0.593
______________________________________
3. Referring to FIGS. 64 to 82(b), Examples (25 to 36) according to
embodiments to attain the second object of the present invention
will be described below. Prior to explanation of examples, the
shape of the information recording medium will be described below
by taking the CD standard as an example, and also by referring to
FIG. 63.
In FIG. 63, the thickness of the substrate of the optical disk
(hereinafter referred to as the information recording medium) 90 is
1.2 mm, and its diameter is 120 mm. The disk has a hole of .phi.15
mm, (a center hole 91), in its center. An area of 26 to 33 mm
diameter outside the hole 91 is the clamping area of a spindle
motor. Regarding the information recording surface, a lead-in area
901 exists from the maximum diameter of 46 mm to the diameter of 50
mm, and a program area 903 continues from the diameter of 50 mm to
the maximum diameter of 116 mm. A lead-out area. 902 continues from
116 to 117 mm from the center. A table of contents (TOC) of the
program area 903 is recorded in the lead-in area 901.
The optical pick-up apparatus 10 which reproduces information from
the information recording medium 90, is held to be accessible in an
area from a lead-in area 901 to a lead-out area 902 of the
information recording medium 90 which is presumed at least to be
reproduced, and is moved by a feed motor. Specifically, when high
speed access is required, it is driven by a linear motor such as a
voice coil motor, or the like.
When information is reproduced, initially, the optical pick-up
apparatus 10 is moved to a position in which the lead-in area can
be read; the objective lens is driven to carry out the focusing
operation and the track-servo operation, and the TOC is read; and
the optical pick-up apparatus 10 is then moved to a predetermined
track according to the TOC information for program
reproduction.
EXAMPLE 25
FIG. 64 shows the structure corresponding to the information
recording medium 90 having a 0.6 mm thickness substrate 904.
In FIG. 64, the luminous flux emerging from the laser beam source 1
passes through the diffraction grating 12 and the beam splitter 13;
it passes through the collimator lens 14 which is a luminous flux
conversion lens, held by a lens frame 141, which is a correction
means and moves in the direction of the optical axis, and becomes
almost parallel luminous flux; and then, the optical path of the
luminous flux is deflected by 90.degree. by the mirror 15. The
luminous flux is limited to a predetermined flux by the diaphragm
147 and then enters into the objective lens 16. The luminous flux,
entered into the objective lens 16, is converged onto the
information recording surface 905 through the substrate 904. The
luminous flux modulated by the information pit and reflected from
the information recording surface 905, returns to the beam splitter
13 through the objective lens 16, the mirror 15, and the collimator
lens 14. Then, the luminous flux is separated from the optical path
of the laser beam source 1, and enters into the light detector 9,
which is a light beam receiving means, through the concave lens
17.
The light detector 9, which is a light beam receiving means, is
composed of multi-divided PIN photodiodes, each element of which
outputs a current proportional to the intensity of the luminous
flux entered into the element. This current is fed to the detection
circuit system, not shown in the drawing, and in this circuit
system, an information signal, a focus error signal and a track
error signal are generated. An objective lens driving means 161
structured by a magnetic circuit, coil, or the like, controls the
objective lens 16 and diaphragm 147, which are integrally provided
with each other, according to the focus error signal and the track
error signal, and is structured so that the optical spot position
is always positioned in the information track.
The optical pick-up apparatus 10 is supported by a guide shaft, not
shown in the drawing, provided on the chassis 41, and is driven by
a feed motor, not shown in the drawing, between a P.sub.IN position
(for example, a position which is 20 mm remote from the center of
the disk), at which the position of the optical axis of the
objective lens 16 is located inside the lead-in area in the inner
and outer peripheral direction of the information recording medium
90, and P.sub.OUT position (for example, a position which is 65 mm
remote from the center of the information recording medium ), the
position at which the optical axis of the objective lens 16 is
located outside the lead-out area.
As the objective lens 16, a lens is used in which the aberration is
corrected so that an excellent optical spot condition (the first
optical spot condition) can be obtained corresponding to the 0.6 mm
thickness substrate, when the parallel luminous flux enters into
the objective lens 16. Accordingly, it is difficult to read the
information recording medium of the 1.2 mm thickness substrate
under this condition, because of increased aberration.
In FIG. 65, when an information recording medium 90 having a 1.2 mm
thickness substrate 906 is read, the optical pick-up apparatus 10
is moved by a feed motor in the inner peripheral direction of the
information recording medium 90. When the position of the optical
axis of the objective lens 16 is located almost inside of the
lead-in area 901 (inside the innermost peripheral position in which
the lead-in area can be read), an extension 142 integrally provided
on the lens frame 141, contacts the first pin 221 fixed on the
chassis 41. The optical pick-up apparatus main body is moved to a
further remote P.sub.IN position, however, the lens frame 141 can
not be moved at the position by interfering with the first pin 221.
The lens frame 141 is moved to the position at which the frame has
the first optical spot condition in the housing of the optical
pick-up apparatus 10, and one end portion of the positioning spring
102 is engaged with the recessed portion provided in the lens frame
141. Then, the lens frame 141 is positioned in the optical pick-up
apparatus 10 main body, and secured.
Although the spherical aberration moves to the
"overcorrected"-range when the thickness of the substrate 904 is
increased, the divergent light is entered into th(e objective lens
16 when the collimator lens 14 is moved to the laser beam source 1
side, and the "under"-spherical aberration is generated by the
objective lens 16, so that the "overcorrected"-spherical aberration
is canceled out. Accordingly, an excellent optical spot condition
(the second optical spot condition) cain be obtained through the
1.2 mm thickness substrate.
In FIG. 66, when the optical system is returned to the first
optical spot condition corresponding to the 0.6 mm thickness
information recording medium, the optical pick-up apparatus 10 is
moved to P.sub.OUT position in the outer peripheral direction, in
which the position of the optical axis of the objective lens 16 is
forwarded over the lead-out area 902 (over the outermost peripheral
position in which the lead-out area can be read), by the feed
motor, not shown in the drawing. The extension 142 provided on the
lens frame 141 interferes with the second pin 222 fixed on the
chassis 41, and from this position, only the optical pick-up
apparatus 10 main body is moved. The lens frame 141 is moved to the
position in which the optical system is again on the first optical
spot condition, and the end portion of the positioning spring 102
is engaged with the other recessed portion provided in the lens
frame 141, so that the lens frame 141 is positioned and secured in
the optical pick-up apparatus 10 main body.
In this example, the reproduction of the 0.6 mm thickness substrate
information recording medium in a plurality of information
recording medium types which can be read by the disk apparatus, is
the first priority. Initially, loading of the information recording
medium 90 is started, and the first condition and the second
condition are detected by a reflection type photosensor 101, which
is a correction condition detection means, depending on whether the
lens frame 141 is located at a predetermined position (the position
of the first optical spot condition) in the optical pick-up main
body. A CPU, or the like, in the information recording medium
apparatus judges whether the position of the lens frame 141 to be
detected is located at the position corresponding to the first
optical spot condition, or not. When the lens frame 141 is not
located at this position, the optical pick-up apparatus 10 is moved
outward to P.sub.OUT, and the collimator lens is moved to the
position on the first optical spot condition. Then, the optical
pick-up apparatus 10 is moved inward, and the reflection type
photosensor 43, which is a read-in position detection means,
detects the extension provided from the lower surface of the
optical pick-up main body. By this detection signal, the optical
pick-up apparatus 10 is positioned so that the lead-in area 901 can
be read, and the focus-search operation is carried out.
When it is judged that the thickness of the information recording
medium is not 0.6 mm, but 1.2 mm, the optical pick-up apparatus is
moved at once so that the optical axis of the objective lens 16 is
located at the P.sub.IN position on the inner periphery side, and
the collimator lens is moved to a position on the second optical
spot condition in the optical pick-up apparatus 10 main body.
As described above, in this example, the correction means in the
optical pick-up apparatus can be driven using the driving force of
the feed motor of the optical pick-up apparatus 10, and it is not
necessary to provide an additional driving means such as a motor,
or the like, to drive the correction means in the optical pick-up
apparatus, resulting in a smaller size, lighter weight, and lower
cost.
EXAMPLE 26
In this example, the correction means is driven only when the
optical system is moved outward so that the position of the optical
axis of the objective lens is located outside the lead-out area
902. A push switch type mechanism, to control the movement of the
correction means, is accommodated in the optical pick-up apparatus
10.
In FIG. 67, a laser unit 19 (a hologram laser unit), which is a
correction means and with which the light detector, beam splitter,
semiconductor laser are integrated, is held in a slide frame 191
which can slide in the emerging direct-on of the laser light, and
is accommodated in a housing of the optical pick-up apparatus
10.
When this slide frame 191 slides, the distance between the position
of the laser beam source and the objective lens 16 is changed, and
the divergent degree of the luminous flux entering into the
objective lens 16 is also changed. Thereby, the aberration of the
optical spot can be corrected in the same way as in Example 25
described before.
The optical pick-up apparatus 10 is supported by 2 guide shafts 26,
and is driven by the linear motor 25 in the direction of inner and
outer periphery of the information recording medium 90.
Then the optical pick-up apparatus 10 is moved to the P.sub.OUT
position at which the optical axis of the objective lens is located
outside the lead-out area 902, an extension 192 of the trailing end
of the slide frame 191 interferes with an extension 223 provided on
the chassis, and the slide frame 191 is pushed into the inner part
of the housing. The slide frame 191 is held and positioned by a
holding pin 104, and is located at a predetermined laser position
on the optical spot condition corresponding to a 1.2 mm thickness
substrate. When the optical pick-up apparatus 10 is moved again to
the P.sub.OUT position at which the optical axis of the objective
lens is located outside the lead-out area 902, the slide frame 191
is pushed again into the inner part of the housing, and the holding
pin 104 is disengaged, so that the sliding frame 191 is located at
the laser position on the optical spot condition corresponding to
0.6 mm thickness substrate.
Referring to FIGS. 68, 69(a) and 69(b), this mechanism will be
detailed below. In FIG. 68, one end of the holding pin 104 is
pressed by the spring 105 on a pin guide 193 integrally formed with
the slide frame 191. The slide frame 191 is pulled toward the lower
left direction in the drawing by the spring 103, and is positioned
in the housing of the optical pick-p apparatus under the condition
that the tip of the holding pin is in contact with a portion A.
When the optical pick-up apparatus is moved until the position of
the optical axis of the objective lens is located at the P.sub.OUT
position, since a extension 192 is integrally formed with the slide
frame 191, this extension 192 is pushed by a extension 223 provided
on the chassis, the tip of the holding pin 104 passes through a
portion B of the pin guide 193, and falls into a portion C (refer
to FIGS. 69(a) and 69(b)). The distance between the portion A and
the portion B is a variable amount for mounting of the slide frame
191.
When the optical pick-up apparatus is moved again until the
position of the optical axis of the objective lens is located at
the P.sub.OUT position, under the condition that the holding pin
104 has fallen into the portion C, the extension 192 is pushed and
the tip of the holding pin 104 is pushed to the portion D of the
pin guide 193. The tip of she holding pin 104 can be moved only in
the direction of the portion E of the pin guide 193. When the force
to push the protrusion 192 is released, the slide frame 191 is
pulled back by the spring 103, and is retreated until the tip of
the holding pin 104 falls into the portion A of the pin guide 193.
As described above, 2 correction conditions respectively
corresponding to 0.6 mm thickness and 1.2 mm thickness can be
reciprocally set each time when the optical pick-up apparatus 10 is
moved to the P.sub.OUT position. As in this example, when the
switching method by which the correction condition is switched
outside the lead-out area 902, is adopted, a large diameter and
large torque spindle motor can be used as the spindle motor 24 to
rotate the information recording medium 90, resulting in obtaining
of stable information.
Although the correction means is driven by the movement of the
optical pick-up apparatus to the P.sub.OUT position in this
example, it may also be structured so that the correction means is
driven by the movement to the P.sub.IN position.
EXAMPLE 27
Three correction conditions of the optical spot are adopted in this
example. The optical spot is corrected when the luminous flux
conversion lens, constituting the correction means located in the
optical path from the laser beam source to the objective lens is
moved, and the correction means are located at 3 positions in the
direction of the optical axis, so that the optical system functions
with the information recording medium substrate thickness of, for
example, 1.2 mm, 0.8 mm, and 0.6 mm.
In FIG. 70, the collimator lens 14, which is a luminous flux
conversion lens, is held by the lens frame 141 incorporating the
extension 192. The collimator lens is slidably mounted on a frame
guide provided in the housing 100 of the optical pick-up apparatus
10, and is pulled downward by the spring 103 and is held at the
position in which the extension 192 comes into contact with a cam
plate 108b. The cam plate 108b rotates on a rotation axis 108
integrally with a rotation plate 108a. Three pins 351, 352, 353,
and three cutouts 361, 362 and 363 are provided on the rotation
plate 108a, and the direction of the rotation of the rotation plate
108a is restricted and held by a holding spring 106.
When the correction condition is switched, the following operations
are carried out: the optical pick-up apparatus 10 is driven to the
inside of the position at which the position of the optical axis of
the objective lens exceeds the lead-in area 901; a pin 351 is
pressed by the extension 107 provided on the chassis; and the cam
plate 108b is rotated to the position at which the cutout 361 is
engaged by the holding spring 106. The lens frame 141 is lowered by
the spring 103 and held by the rotation of the cam plate 108b. When
this operation is repeated, the lens position is respectively set
at 3 positions in the direction of the optical axis. In this
connection, the extension 107 is structured as follows. The
extension 107 is pivotally supported on the chassis so that it can
be rotated, and when the optical pick-up apparatus 10 returns to
the lead-in area, it can not interfere with the pin B.
When a method to switch the correction means inside the lead-in
area 901 is adopted, the necessary amount of movement required for
driving the correction means, after the discrimination of the type
of information recording medium 90 in the read-in portion, is
shorter, and the time required for starting the reproduction is
also shorter.
EXAMPLE 28
In FIG. 71, the laser beam source 1, the beam splitter 13, and the
light detector 9 are held in an integrally formed frame 112 which
can move in the direction of the optical axis, and constitute the
correction means. A portion 272 of a warm wheel is formed in the
frame 112. A holding member 113 is provided in the housing of the
optical pick-up apparatus 10, and holds the frame 112 in the
movement direction by friction. The portion 272 of the worm wheel
is engaged with a worm 271 driven by the motor 27 mounted on the
chassis 41, at such a position that the optical pick-up apparatus
10 can read the lead-in area 901. When the frame 112 is moved in
the direction of the optical axis of the objective lens 16, the
correction of the optical spot can be carried out.
When the lead-in area 901 is read at the position of the laser beam
source 1 corresponding to the optical spot condition appropriate
for reading a predetermined information recording medium, and it is
judged that the disk is not an acceptable predetermined disk, then,
the worm 271 is rotated by the motor 27, the frame 112 is driven,
and the position of the laser beam source 11 is correspondingly
moved.
The movement of the position of the laser beam source 1 can be
carried out at least under the condition that the focus-servo
operation is ON, the frame 112 can be continuously moved and can
hold components. When the frame 112 is driven by the motor during
the reading process, the position of the laser beam source 1 can be
set so that the quality of the information signal to be read and
the track error signal becomes best.
When writing onto the information recording medium is carried out,
it is preferable that the frame is driven during test-writing so
that the optical spot condition, under which the optical spot
condition for writing is optimum, is obtained, and the laser beam
source is set at the position in which the emergent light beam
power required for writing is at a minimum.
EXAMPLE 29
FIG. 72 shows an example of a separate optical system method in
which the objective lens 16, the objective lens drive means 161, a
mirror to guide the laser beam to the objective lens, and the
correction lens 17 are mounted on a movable carriage 251 when the
information recording medium 90 is given access in the direction of
the inner and outer periphery, and the laser beam source 1, beam
splitter 13, collimator lens 14, light detector 9 etc., are fixed
on the chassis as a fixed optical system 111.
The carriage 251 is supported by 2 guide shafts 26, and driven by 2
linear motors at high speed. When this separate optical system is
used, the weight of the movable portion is decreased, and the
average access time, for example, can be reduced to less than 100
ms. The correction means to cope with the difference of the
thickness of the information recording medium 90, is composed of a
correction lens 17 (concave lens), and when this correction lens is
moved in the direction of the optical axis, an apparent position of
the light beam source of the luminous flux entering into the
objective lens 16 is shifted and the aberration of the optical spot
is corrected. The motor 27, which is the driving means for the
correction means, is mounted on the chassis, and moves the carriage
251 to the lead-in area 901 or inside the lead-in area, and moves
the correction lens 17 by the engagement of a clutch 273. The power
transmission mechanism from the clutch 273 to the lens frame 141
can be composed of widely known mechanical elements such as a belt,
or the like. Alternatively, as described in the Examples above, the
correction means may be driven by the movement of the optical
components which exceeds the lead-in area or the lead-out area of
the information recording medium 90, without using the motor
27.
In the drive of the movable portions which are accessible at high
speed, it is necessary to set a broader control range, and it is
essential that no high-order resonance, pitching, rolling, or
yawing is generated in several kHz range. When the above pitching,
etc., is generated when the center of gravity, in the plane
perpendicular to the direction of movement, does not coincide with
the generation point of the driving force of the linear motor 25.
Therefore, it is desirable that 2 linear motors 25 are used, and
located so that the generation points of their driving force are
symmetrical with respect to the center of gravity, and the center
of gravity of the correction means is not moved in the plane
perpendicular to the direction of movement even during
correction.
In this example, although the condition of the optical spot is
corrected by moving the correction lens 17 constituting the
correction means in the direction of the optical axis, it may also
be structured by insertion and removal of a concave lens into the
luminous flux entering into the objective lens 16; insertion and
removal of the parallel planes in the convergent luminous flux
forwarding from the objective lens 16 to the information recording
medium 90; and a change of the diaphragm diameter for the luminous
flux forwarding the objective lens 16. At this time, it is also
necessary that the correction means is arranged in the direction in
which the center of gravity of the movable portion is not
moved.
EXAMPLE 30
Although the correction methods in the above Examples are carried
out by correction of the movement of the lens and the laser beam
source in the direction of the optical axis, the correction means
may also be structured as follows.
In FIG. 73, the correction lens, which is a correction means, is
inserted into and removed from the optical path from the laser beam
source (a hologram laser unit 19 in this example) to the objective
lens 16. This correction lens is provided to correct any aberration
due to the difference of the substrate thickness of the information
recording medium 90. In cases where the information recording
medium 90 having a thicker substrate (for example, 1.2 mm) is read
by the objective lens corresponding to the thinner substrate (for
example, 0.6 mm) in this example, a lens having the concave lens
function is inserted into the optical path. When the information
recording medium 90 having the thinner substrate (for example, 0.6
mm) is read by the objective lens corresponding to the thicker
substrate (for example, 1.2 mm), a lens having the convex lens
function is inserted into the optical path.
This lens is held by a rotating frame 171 which can be rotated
around the rotation shaft 172, and the lens is inserted into and
removed from the optical path by rotating the rotating frame 171.
The rotation shaft 172 rotates perpendicular to the direction in
which the optical pick-up apparatus 10 is moved by the feed motor
in the direction of the inner and outer periphery of the
information recording medium 90, and thereby, jolting generated
when the optical pick-up is driven by the feed motor, is reduced.
Thereby, the following disadvantages in which the optical axis
entering into the objective lens is shifted due to this jolting;
the position of the optical spot is also shifted; and specifically,
the tracking becomes unstable.
EXAMPLE 31
In FIG. 74, the parallel planes 143, which are a correction means,
are inserted into and removed from the convergent luminous flux
entering from the objective lens 16 to the information recording
medium 90. For the objective lens 16, a lens, the aberration of
which is corrected with respect to the 1.2 mm thickness substrate,
is used, for example, when the information recording medium formed
of 0.6 mm thickness substrate is reproduced, a 0.6 mm thickness
parallel plane 143, corresponding to the difference of the
thickness, is inserted. Although the optimum thickness of the
parallel plane is a little different depending on the refractive
index, the refractive index of generally used parallel plane is
about 1.52, and is almost the same as that of the disk substrate.
Accordingly, the thickness of the plane to be inserted may be equal
to only the difference of the thickness. In FIG. 75, a parallel
plane insertion and removal mechanism is provided on the upper
surface of the objective lens driving means 161. FIG. 75 is a
drawing viewed from the information recording medium 90 side. The
parallel plane 143 is held by a rotation frame 71 which can be
rotated around the shaft 172, and the rotational direction of the
rotation frame is restricted by a hook 144, and the rotation frame
is held by the hook.
When the optical pick-up apparatus 10 is moved inside the lead-in
area and the G portion is pushed by an extension on the chassis,
not shown in the drawing, the hook 144 is disengaged. Then, the
rotation frame 171 is rotated around the shaft 172 by the spring,
not shown in the drawing, and comes into contact with the fixing
pin 145. Thereby, the parallel plane 143 stops on the upper surface
of the objective lens 16 (shown by a dotted line in the drawing)
The optical pick-up apparatus 10 is moved outside the lead-out area
in the direction of the outer periphery, and an F portion is pushed
by the second extension on the chassis, not shown in the drawing,
thereby, the rotation frame 171 is rotated. When tie rotation frame
171 is engaged again by the hook 144, the parallel plane 143 is
held at a position out of the optical path.
EXAMPLE 32
In FIG. 76, an objective lens driving means 161, by which a
plurality of objective lenses constituting the correction means are
integrally driven, is used, and when the objective lens driving
means 161 is moved in the direction perpendicular to the optical
axis of the objective lens with respect to the housing 100 of the
optical pick-up apparatus 10 having the laser bear source (in this
example, the hologram laser unit 19), corresponding to the type of
the information recording medium 90, one of the plurality of
objective lenses is selected.
The objective lens driving means 161 is composed of: a fixing
portion 162 having a magnetic circuit composed of a magnet, a yoke,
etc.; a movable portion 163 on which a focusing coil and a tracking
coil are mounted; the first objective lens 16a and the second
objective lens 16b which are adhered and fixed onto the movable
portion 163; and a wire to movably support the fixing portion 162
and the movable portion 163 in the focusing direction and the
tracking direction, or the like.
The aberration of the first objective lens 16a is minimized under
the condition of 1.2 mm substrate thickness when the parallel
luminous flux enters into the objective lens, and the aberration of
the second objective lens 16b is also minimized under the condition
of 0.6 mm substrate thickness.
The hologram laser unit 19 integrally provided with the laser beam
source, the beam splitter, and the light detector, is fixed in the
main body housing 100 of the optical pick-up apparatus 10. The
housing 100 is supported on the chassis by the movable guide member
126 in the direction of the inner and outer periphery of the
information recording medium 90, and is driven by the feed
motor.
The objective lens driving means 161 is movably held on the housing
100 in the direction perpendicular to the optical axis of the
objective lens, and can move at least within the distance between 2
objective lenses. Any moving method, such as parallel movement, or
rotation, may be adopted, and actually, any method by which 2
objective lenses are respectively positioned on the optical axis of
the laser, may be acceptable.
When an object to be read, at a predetermined priority, by the
information recording medium apparatus is an information recording
medium having 0.6 mm substrate thickness, the optical pick-up
apparatus 10 is driven outside the lead-out area in the direction
of the outer periphery by the feed motor concurrently with the
information recording medium 90 loading; the objective lens driving
means 161 is pushed by the extension provided on the chassis, and
is moved with respect to the housing 100 of the optical pick-up
apparatus 10; and the second objective lens 16b is positioned on
the optical axis of the laser.
After that, the optical pick-up apparatus 10 is moved into the
lead-in area by the feed motor, and tries to read. When the
information recording medium 90 is not a predetermined 0.6 mm
thickness substrate, the optical pick-up apparatus 10 is moved at
once to the inner periphery inside the lead-in area by the feed
motor; the objective lens driving means 161 is pushed by another
extension on the chassis and is moved with respect to the housing
100 of the optical pick-up apparatus 10; and the first objective
lens 16a is positioned on the optical axis of the laser. After
that, the optical pick-up apparatus 10 is returned to the lead-in
area by the feed motor, and tries to read again.
EXAMPLE 33
This example is structured as follows. The same objective lens
drive means 161 and housing 100 of the optical pick-up apparatus 10
as these in Example 32 are used. In example 32, the housing 100 is
guided by the guide member 126 which supports the optical pick-up
apparatus movably in the direction of toe inner and outer periphery
of the information recording medium 90 on the chassis, but this is
replaced by a method in which the objective lens drive means 161 is
guided by the guide member 126 in this Example.
In FIG. 77, the fixing portion 162 of the objective lens driving
means 161 is supported by the guide member 126 on the chassis so
that it can be moved in the direction of the inner and outer
periphery of the information recording medium 90, and is driven by
the feed motor. The housing 100 having the hologram laser unit 19
is held below the objective lens driving means 161 so that it can
move in the arrowed direction in the drawing, and can be moved
horizontally at least by the distance between the 2 objective
lenses. When the housing is moved, one of the 2 objective lenses is
positioned on the optical axis of the laser, and the objective lens
corresponding to the substrate thickness of the information
recording medium 90 is selected, so that the optimum optical spot
can be converged onto the information recording surface of the
information recording medium.
EXAMPLE 34
In FIG. 78, the objective lens driving means 161 for integrally
driving a plurality of objective lenses, and a mirror 15 by which
the optical path is bent by 90.degree. between the objective lens
driving means 161 and the laser beam source (in this example, the
hologram laser unit), are used. The mirror 15, constituting the
correction means, is moved in the direction of the optical axis of
the laser beam corresponding to the type of the information
recording medium 90, by the distance corresponding to the interval
between a plurality of objective lenses.
In FIG. 78, the objective lens driving means 161 is composed of: a
fixing portion 162 having a magnetic circuit composed of a magnet,
a yoke, etc.; a movable portion 163 on which a focusing coil and a
tracking coil are mounted; the first objective lens 16a and the
second objective lens 16b which are adhered and fixed onto the
movable portion 163; and a wire to movably support the fixing
portion 162 and the movable portion 163 in the focusing direction
and the tracking direction, or the like.
The aberration of the first objective lens 16a is minimized under
the condition of 1.2 mm substrate thickness when the parallel
luminous flux enters into the objective lens, and the aberration of
the second objective lens 16b is also minimized under the condition
of 0.6 mm substrate thickness.
In the housing 100, the laser beam source, the beam splitter, the
hologram laser unit 19, integrally provided with a light detector,
the collimator lens 14, which converts the diverged luminous flux
from the laser into a parallel luminous flux, and a mirror 15,
which is movably supported in the advancing direction of the
parallel luminous flux, and which bends the direction, in which the
luminous flux advances, by 90.degree. and directs the luminous flux
to the objective lens, are accommodated. When the mirror 15 located
at the position shown by a solid line in the drawing, the luminous
flux from the laser enters into the second objective lens 16b, and
reads the information recording medium having a 0.6 mm thickness
substrate.
When the mirror 15 is moved to the position shown by a dotted line
in the drawing, the luminous flux from the laser enters into the
first objective lens 16a, and is appropriate for reading out the
information recording medium 90 having a 1.2 mm thickness
substrate.
The alignment of the 2 objective lenses may be any of the
following: radial to the information recording medium 90;
tangential; or at some angle with respect to either of the above
two alignments. However, when the 2 objective lenses are aligned in
the tangential direction, this alignment is preferable because
there is a most surplus room inside the inner periphery of the
disk. In this case, the direction of movement of the mirror 15 is
perpendicular to the direction of the movement of the optical
pick-up apparatus in the direction of the inner and outer
periphery. Accordingly, it is easy to prevent the mirror from being
jolted when the optical pick-up apparatus is driven by the feed
motor.
EXAMPLE 35
The condition of the optimum optical spot is different
corresponding to the difference of the information recording
density (the shortest pit length, the track pitch) according to the
type of information record medium. It is preferable that the
optical spot size is adjusted so that the spherical aberration
becomes minimum with respect to the difference of the substrate
thickness, and that the optical spot size is optimally adjusted
with respect to the difference of the recording density.
In the example shown in FIG. 79, the following correction means is
provided: the spherical aberration generated corresponding to the
difference of the substrate thickness of the disk is corrected by
the movement of the hologram laser unit 19 in the direction of the
optical axis; and the spot size is corrected by the adjustment of
the diaphragm diameter of the diaphragm 147 which is provided on
the optical path from the laser beam source to the objective lens
16. As a diaphragm means, the following are acceptable: an iris
diaphragm 148 widely used for camera lenses, or the like, as shown
in FIG. 80(a); insertion bad rotation of the single diaphragm 147
around the shaft 172 as shown in FIG. 80(b), or the like. In the
case of FIG. 80(b), when this diaphragm 17 is not set into the
position, the luminous flux is limited by another diaphragm 147
integrally provided on the movable portion of the objective lens
driving means 161.
When there are few types of information recording mediums to be
read, and 2 diaphragm diameters are used for the purpose, the
insertion and removal method as shown in FIG. 80(b) is simple to
use. When 3 types of diaphragm diameters are necessary or fine
adjustment is carried out, the iris diaphragm 148 as shown in FIG.
80(a) is simpler for use. Adjustment or insertion and removal of
the diaphragm means can be attained when mechanical elements such
as gears, links, etc., are used and these are interlocked with the
movement of the hologram laser unit.
EXAMPLE 36
When the track error is detected by the 3-beam method, a main spot
for reading is converged onto the information recording surface of
the information recording medium, and 2 sub-spots are respectively
converged into positions which are respectively shifted by 1/4 of
the track with respect to the track, and an amount of the reflected
light of the 2 sub-spots is detected by the light detector.
In FIGS. 81(a) and 81(b), when the distance between the main spot
and the 2 sub-spots are respectively 20 mm, and the track pitch is
0.84 mm, an angle formed between the direction of alignment of 3
spots and the track, is optimally 0.60 (FIG. 81(a)). In an
information recording medium having different track pitches, for
example, for an information recording medium having 1.6 mm track
pitch, the optimum angle is 1.15.degree. (FIG. 81(b)). When this
angle is not appropriate, the amplitude of the track error signal
is decreased, and the track follow-up property is lowered.
In this example, the azimuth of 3-spots converged onto the
information recording medium is corrected with respect to the track
of the information recording medium, and a diffraction grating, the
angle of which is adjustable, is provided in the optical path from
the laser beam source to the beam splitter, and the azimuth of the
lattice of the diffraction grating, which is the correction means,
is corrected.
In FIGS. 82(a) and 82(b), the following methods are adopted as the
rotation method of the diffraction grating 12. The diffractive
grating 12 is held in the cylindrical holder 121, and the holder
121 is rotated in the housing of the optical pick-up (FIG. 82(a);
or the diffraction grating 12 is held by one end of the lever 123
which rotates around the rotation shaft 122, and the entire lever
is rotated 82(b). When the rotation of the diffraction grating 12
is interlocked with the correction means of the difference of the
thickness of the disk or the diaphragm means, an information
recording medium apparatus is realized, in which both an SD disk
and a CD disk, having respectively different substrate thickness
and track pitch information recording density, can be
satisfactorily reproduced.
According to the present invention, the drive of the correction
means provided for the optical pick-up apparatus which reads the
information recording medium, having a different substrate
thickness or a different track pitch information recording density,
can be carried out using the driving force of the feed motor,
without providing any further motor, solenoid, or the like, so that
the overall size of the optical pick-up is reduced, and its weight
and cost can be correspondingly reduced.
Further, when the correction means is driven using the motor
provided on the chassis in the lead-in area, the size and weight
can be reduced. Furthermore, when the direction of movement or
support of the correction means is different from the direction for
access of the optical pick-up apparatus, jolting can be prevented,
so that the focusing and tracking control can be securely carried
out. Specifically, in the structure for the high speed access, the
center of gravity of the carriage is not changed even when the
correction condition is changed by the correction means, resulting
in the prevention of resonance.
Thus, as described above, an information recording medium apparatus
in which plural types of information recording mediums can be
reproduced by one apparatus, can be realized.
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